SQL(Structured Query Language)

Structured Query Language (SQL) provides the ability to create and define relational database objects. After these objects are defined, the language permits one to add data to these objects. Once data has been added, one can modify, retrieve, or delete that data. The language provides the capability of defining what type of authority one might have when accessing the data.

Data Definition Language

As the name implies, there is a group of SQL statements that allows one to define the relational structures that will manage the data placed in them. The “CREATE” statements brings Relational Database Management System (RDMS) objects into existence. The types of objects one can create are STOGROUP, Database, Table space, Table, Index, View, Synonym, and Alias. The definitions of these objects are as follows:

STOGROUP: A storage group is a list of disk volume names to which one can assign a name. One defines the list of disk volumes and assigns the STOGROUP name with the Create STOGROUP statement.

Database: A database is a logical structure in which tables and indexes are later created. The database is defined and associated with a STOGROUP with a Create Database statement.

Tablespace: A tablespace is an area on disk that is allocated and formatted by the Create Table space statement.

Table: A table is an organizational structure which is defined in a Create Table statement. In this statement, the data attributes are defined by column, giving each column its own unique name within the table.

Index: A index is used in conjuction with the “Primary Key” parameter of the Create Table statement. It is made with the Create Index statement and provides the duplicate record-checking necessary for a unique key.

View: A view is an alternative perspective of the data present in a database. It is made with the Create View statement and can represent a subset of the columns defined in a table. It can also represents a set of columns combined from more than one table.

Synonym: The Create Synonym statement defines an unqualified name for a table or a view.

Alias: The Create Alias statement defines an alternate qualified name for a table or a view.

After a table is created, additional columns may be added with an Alter Table statement. Any RDMS object that was made with a create statement can be removed with a drop statement.

In order to define RDMS objects, one needs various levels of authority. The following is a list of authority levels that can be granted to a user ID to operate on a designated database.

DBADM                Database administrator authority

DBCTRL              Database control authority

DBMAINT             Database maintenance authority

CREATETS         Create Table space Authority

CREATETAB       Create Table authority

DROP                  Drop authority on a database or subordinate objects

Data Manipulation Language

                There are four SQL data manipulation statements(DML) available: Insert, Select, Update, and Delete. After tables are defined, they are ready to store data. Data is added to tables through the SQL Insert statement. Once data has been inserted into a table, it can be retrieved by the use of the Select statement. Data stored in a table can be modified by executing the SQL Update statement. Data can be deleted from a table by using the SQL Delete statement.

                The SQL statements perform RDMS operations that can affect only one row at a time if desired. The same statements can, if required, affect many or all of the rows in a table. It is possible to select one row and insert it into another with one statement. It is also just as easy to select all of the rows from one table and insert all of them into another with a single statement. The same scope of operation applied to the update and delete statements. The scope of operation is controlled by the use of the WHERE clause. The operation will affect only the rows that satisfy the search condition. When no search condition specified, the entire table is affected.

                There are additional language elements available that provide the ability to process the table data while it is being retrieved. In addition, there are a variety of functions that modify the value of the data that is returned in a query. There are column functions that act on all of the values of the selected rows for a specified column and return a single answer. There are also scalar functions that return a specific answer for each row that satisfies the search condition.

                As mentioned previously, SQL provides the ability to filter what data is retrieved in a select statement by including the WHERE clause. The WHERE clause specifies a variety of comparisons between two values. The values could be column values or the result of an operation involving more than one column or a constant. The comparison operation are the same as those used in COBOL, with the exception of two additional operators. The first is the IN operator that compares a single value has a match in the specified list of values. The other is the LIKE operator, in which you can specify a value string that includes “wildcard” characters in such a manner that you can select rows of a table where column values are similar to the extent you require.

                SQL provides four arithmetic operations : addition, subtraction, multiplication, and division. An arithmetic _expression may involve any combination of column name or numbers. The arithmetic _expression may itself be used as a column name or in a Select, Insert, Update, or Delete statement.

                SQL provides the ability to sort the data retrieved from a table via the ORDER BY clause. In this clause, you can specify one or more sort column names as well as if each sort key is ascending or descending.

                SQL also provides the ability to perform set manipulation operations. Using SQL, one can SELECT the intersection of two or more sets of data by coding a JOIN. A JOIN is any SELECT statement that has more than one DBMS object listed in its FROM clause. One can combine different sets of data by using the UNION operator. Other set manipulations can be executed by combining different operators and search conditions.

The Following are the most frequently asked questions....

  Q1)  What RDMS objects are created with the SQL CREATE statements?

  A1)  The SQL CREATE statements are used to create the following objects:

                STOGROUP         A storage group

                DATABASE           A logical collection of tables

                TABLESPACE      An area that stores tables

                TABLE                   A data structure organized by a specified columns

                INDEX                   An alternate path to a table data

                VIEW                     An alternate representation of one or more tables

                SYNONYM            An alternate name for local table or view

                ALIAS                    An alternate name for a table definition which may be local   or remote, existence or nonexistent

  Q2)  What RDMS objects are required before you can create a table?

  A2)  Before you can create a table, you need an existing database and tablespace.

  Q3)  In what RDMS object does one first list column names?

  A3)  One first uses the column name in the CREATE TABLE statement.

  Q4)  What is the syntax for a CREATE TABLE statement?

  A4)  CREATE TABLE table name

                                (column name list

                                primary key (column name))

                                in database-name, tablespace-name.

  Q5)  Can one add columns to a table after it has been defined?

  A5)  Yes, one can add column to a table after it has been defined by using the SQL ALTER TABLE statement.

  Q6)  Where in a table are added columns located?

  A6)  The new columns are added to the end of the table.

  Q7)  After a table is defined, can columns be removed?

  A7)  The only way to remove columns from an existing table involves a migration program that extracts only the desired  

columns of data, redefining the table without the unwanted columns, then populating the new table. One have to handle

all the old table’s dependents programmatically.

  Q8)  Which RDMS objects can you change with the SQL ALTER statements?

  A8)  The SQL ALTER statement can change a table index, a table, a tablespace, or a STOGROUP.  

  Q9)  What authority is required to create a table?

  A9)  In order to create tables, one needs CREATETAB privileges.

  Q10)    What is minimum authority required for one to create a tablespace?

  A10)     In order to create tablespaces, one needs CREATETS privileges.

  Q11)    When is it necessary to create a table index?

  A11)     It is necessary to create a table index whenever you want to enforce the uniqueness of the table’s primary key.

  Q12)    What is a synonym?

  A12)     A synonym is an unqualified alternative name for a table or view.

  Q13)    What is a foreign key?

  A13)     A foreign key is the key defined in one table to reference the primary key of a reference table. This foreign key must  

have the same structure as the reference table’s primary key.

  Q14)    What is referential integrity?

  A14)     Referential integrity is the automatic enforcement of referential constraints that exist between a reference table and a  

referencing table. When referential integrity is enforced, the value of a foreign key exists as  a primary key value in the

reference table. In other words, when referential integrity is enforced, all of the foreign key values in, for example, the 

“department code” column in an “employee” table exist as primary key values in a “department” table.

  Q15)    What are the column name qualifiers?

  A15)     A column name qualifier are used as a table designator to avoid ambiguity when the column names referenced exists  

in more than one table used in the SQL statement. Column name qualifiers are also used in correlated references.

  Q16)    What is a correlation name?

  A16)     A correlation name is a special type of column designator that connects specific columns in the various levels of a  

multilevel SQL query.

  Q17)    What is a results table?

  A17)     A result table is the product of a query against one or more tables or views (i.e., it is the place that holds the results of a  

query).

  Q18)    What is a cursor?

  A18)     A cursor is a named control structure used to make a set of rows available to a program. DB2 is the relational database  

system that runs in an MVS environment. It was developed by IBM and interfaces with SQL. With the use of SQL

DB2, databases can be accessed by a wide range of host languages. SQL is the relational database " application

language " that interfaces with DB2. Because of its capabilities, SQL and, in turn, DB2 have gained considerable

acceptance. Thus, a working knowledge of DB2 increases one's marketability.

  Q19)    What is the basic difference between a join and a union?  

  A19)           A join selects columns from 2 or more tables. A union selects rows.   

  Q20)    What is normalization and what are the five normal forms?  

  A20)     Normalization is a design procedure for representing data in tabular format.  The five normal forms are progressive  

rules to represent the data with minimal redundancy.

  Q21)    What are foreign keys?  

  A21)     These are attributes of one table that have matching values in a primary key in another table, allowing for relationships  

between tables.

  Q22)    Describe the elements of the SELECT query syntax?  

  A22)     SELECT element FROM table WHERE conditional statement.  

  Q23)    Explain the use of the WHERE clause?  

  A23)     WHERE is used with a relational statement to isolate the object element or row.  

  Q24)    What techniques are used to retrieve data from more than one table in a single SQL statement?  

  A24)     Joins, unions and nested selects are used to retrieve data.  

  Q25)    What is a view? Why use it?  

  A25)     A view is a virtual table made up of data from base tables and other views, but not stored separately.  

  Q26)    Explain an outer join?  

  A26)     An outer join includes rows from tables when there are no matching values in the tables.  

  Q27)    What is a subselect?  Is it different from a nested select?  

  A27)     A subselect is a select which works in conjunction with another select. A nested select is a kind of subselect where the  

inner select passes to the where criteria for the outer select.

  Q28)    What is the difference between group by and order by?  

  A28)     Group by controls the presentation of the rows, order by controls the presentation of the columns  for the results of the  

SELECT statement.

  Q29)    What keyword does an SQL SELECT statement use for a string search?  

  A29)     The LIKE keyword allows for string searches.  The % sign is used as a wildcard.  

  Q30)    What are some SQL aggregates and other built-in functions?  

  A30)     The common aggregate, built-in functions are AVG, SUM, MIN, MAX, COUNT and DISTINCT.  

  Q31)    How is the SUBSTR keyword used in SQL?  

  A31)     SUBSTR is used for string manipulation with column name, first position and string length used as arguments.  E.g.  

SUBSTR (NAME, 1 3) refers to the first three characters in the column NAME.

  Q32)    Explain the EXPLAIN statement?  

  A32)           The explain statement provides information about the optimizer's choice of access path of the SQL.  

  Q33)    What is referential integrity?  

  A33)     Referential integrity refers to the consistency that must be maintained between primary and foreign keys, i.e. every  

foreign key value must have a corresponding primary key value. 

  Q34)    What is a NULL value?  What are the pros and cons of using NULLS?  

  A34)     A NULL value takes up one byte of storage and indicates that a value is not present as opposed to a space or zero  

value.  It's the DB2 equivalent of TBD on an organizational chart and often correctly portrays a business situation. 

Unfortunately, it requires extra coding for an application program to handle this situation.

  Q35)    What is a synonym?  How is it used?  

  A35)     A synonym is used to reference a table or view by another name.  The other name can then be written in the  

application code pointing to test tables in the development stage and to production entities when the code is migrated. 

The synonym is linked to the AUTHID that created it.

  Q36)    What is an alias and how does it differ from a synonym?  

  A36)     An alias is an alternative to a synonym, designed for a distributed environment to avoid having to use the location  

qualifier of a table or view.  The alias is not dropped when the table is dropped.

  Q37)    When can an insert of a new primary key value threaten referential integrity?  

  A37)     Never. New primary key values are not a problem.  However, the values of foreign key inserts must have  

corresponding primary key values in their related tables. And updates of primary key values may require changes in

foreign key values to maintain referential integrity.

  Q38)    What is the difference between static and dynamic SQL?  

  A38)     Static SQL is hard-coded in a program when the programmer knows the statements to be executed.  For dynamic SQL  

the program must dynamically allocate memory to receive the query results.

  Q39)    Compare a subselect to a join?  

  A39)     Any subselect can be rewritten as a join, but not vice versa. Joins are usually more efficient as join rows can be  

returned immediately, subselects require a temporary work area for inner selects results while processing the outer

select.

  Q40)    What is the difference between IN subselects and EXISTS subselect?  

  A40)     If there is an index on the attributes tested an IN is more efficient since DB2 uses the index for the IN.  (IN for index is  

the mnemonic).

  Q41)    What is a Cartesian product?  

  A41)     A Cartesian product results from a faulty query.  It is a row in the results for every combination in the join tables.  

  Q42)    What is a tuple?  

  A42)     A tuple is an instance of data within a relational database.  

  Q43)    What is the difference between static and dynamic SQL?  

  A43)           Static SQL is compiled and optimized prior to its execution; dynamic is compiled and optimized during execution.  

  Q44)    Any SQL implementation covers data types in couple of main categories. Which of the following are those data  

types ? (Check all that apply)

A). NUMERIC  

B). CHARACTER  

C). DATE AND TIME  

D). BLOBS   E. BIT

  A44)     A,B,C. Not all SQL implementations have a BLOB or a BIT data types.  

  Q45)    We have a table with a CHARACTER data type field. We apply a ">" row comparison between this field and  

another CHARACTER field in another table. What will be the results for records with field value of NULL?

(Check one that applies the best)

  A.      TRUE   

  B.       B. FALSE   

  C.       C. UNKNOWN   

  D.      D. Error.  

  E.       E. Those records will be ignored  

  A45)     C. NULL in a row when compared will give an UNKNOWN result.  

  Q46)    Any database needs to go through a normalization process to make sure that data is represented only once. This  

            will eliminate problems with creating or destroying data in the database. The normalization process is done

            usually in three steps which results in first, second and third normal forms. Which best describes the process to

            obtain the third normal form? (Check one that applies the best)

  A.      Each table should have related columns.    

  B.       Each separate table should have a primary key.    

  C.       We have a table with multi-valued key. All columns that are dependent on only one or on some of the keys should be moved in a different table.

  D.      If a table has columns not dependent on the primary keys, they need to be moved in a separate table.    

  E.       E. Primary key is always UNIQUE and NOT NULL.  

  A46)     D. All columns in a table should be dependent on the primary key. This will eliminate transitive dependencies in  

which A depends on B, and B depends on C, but we're not sure how C depends on A.

  Q47)    SQL can be embedded in a host program that uses a relational database as a persistent data repository. Some of  

the most important pre-defined structures for this mechanism are SQLDA ("SQL Descriptor Area") and

SQLCA ("SQL Communications Area") SQLCA contains two structures - SQLCODE and SQLSTATE.

SQLSTATE is a standard set of error messages and warnings in which the first two characters defines the class

and the last three defines the subclass of the error. Which of the following SQLSTATE codes is interpreted as

"No data returned"?(Check one that applies the best) 

A). 00xxx  

B). 01xxx 

C). 02xxx  

D). 22xxx  

E). 2Axxx

  A47)     C. 00 - is successful completion, 01 - warnings, 22 - is data exception and 2A is syntax error. The SQLSTATE code  

format returned for "No data returned" is "02xxx".

  Q48)    What are common SQL abend codes? (e.g. : 0,100 etc.,)

  A48)     -818 time stamp mismatch

-180 wrong data moved into date field

  Q49)    What is meant by dynamic SQL?

  A49)     Dynamic SQL are SQL statements that are prepared and executed within a program while the program is executing.  

The SQL source is contained in host variables rather than being hard coded into the program. The SQL statement may

change from execution to execution.

  Q50)    What is meant by embedded SQL?

  A50)     They are SQL statements that are embedded with in application program and are prepared during the program

 preparation process before the program is executed. After it is prepared, the statement itself does not change(although

values of host variables specified within the statement might change).

  Q51)    What is meant by entity integrity?

  A51)     Entity integrity is when the primary key is in fact unique and not null.

  Q52)    What will EXPLAIN do?

  A52)     EXPLAIN obtains information (which indexes are used, whether sorting is necessary, which level of locking is  

applied) about how SQL statements in the DBRM will be executed, inserting this information into the 

“X”.PLAN.TABLE where the “X” is the authorization ID of the owner of the plan.

  Q53)    What is the foreign key?  

  A53)     A foreign key is a column (or combination of columns) in a table whose values are required to match those of the  

primary key in some other table.

  Q54)    What will GRANT option do?

  A54)     It will grant privileges to a list of one or more users. If the GRANT option is used in conjunction with the “PUBLIC”  

option, then all users will be granted privileges. Also you can grant privileges by objects and types.

  Q55)    What does the term “grant privileges” mean?

  A55)     Grant privileges means giving access/authority to   DB2 users.

  Q56)    What is an image copy?

  A56)     It is an exact reproduction of all or part of a tablespace. DB2 provides utility programs to make full-image copies (to  

copy the entire tablespace) or incremental image copies to copy only those pages that have been modified since the last

image copy.

  Q57)    What is meant by an index?

  A57)     An index is a set of row identifiers (RIDs) or pointers that are logically ordered by the values of a column that has  

been specified as being an index. Indexes provide faster access to data and can enforce uniqueness on the row in a

table.

  Q58)    What is an index key?

  A58)     It is a column or set of columns in a table used to determine the order of index entries.

  Q59)    What is a join?

  A59)     A join is a relational operation that allows retrieval of data from two or more tables based on matching columns  

values.

  Q60)    What is meant by locking?

  A60)     Locking is a process that is used to ensure data integrity. It also prevents concurrent users from accessing inconsistent  

data. The data (row) is locked until a commit is executed to release the updated data.

  Q61)    What is meant by null?

  A61)     This is a special value that indicates the absence of data in a column. This value is indicated by a negative value,  

usually -1.

  Q62)    What is an object?

  A62)     An object is anything that is managed by DB2 (that is databases, table spaces, tables, views, indexes or synonyms), but  

not the data itself.

  Q63)    Describe referential integrity?

  A63)     Referential integrity refers to a feature in DB2 that is used to ensure consistency of the data in the database.

  Q64)    Describe a primary key?

  A64)     A primary key is a key that is unique, non-null, and is part of the definition of a table. A table must have a primary key  

to be defined as a parent.

  Q65)    How would you find out the total number of rows in a table? - GS

  A65)     Use SELECT COUNT(*) ...

  Q66)    How do you eliminate duplicate values in SELECT? - GS

  A66)     Use SELECT DISTINCT ...

  Q67)    How do you select a row using indexes? - GS

  A67)     Specify the indexed columns in the WHERE clause.

  Q68)    What are aggregate functions?

  A68)     Bulit-in mathematical functions for use in SELECT clause.

  Q69)    How do you find the maximum value in a column? - GS

  A69)     Use SELECT MAX(...

  Q70)    Can you use MAX on a CHAR column?

  A70)     YES.

  Q71)    My SQL statement SELECT AVG(SALARY) FROM EMP-TABLE yields inaccurate results. Why?

  A71)     Because SALARY is not declared to have Null’s and the employees for whom the salary is not known are also  

counted.

  Q72)    How do you retrieve the first 5 characters of FIRSTNAME column of EMP table?

  A72)     SELECT SUBSTR(FIRSTNAME,1,5) FROM EMP;

  Q73)    How do you concatenate the FIRSTNAME and LASTNAME from EMP table to give a complete name?

  A73)     SELECT FIRSTNAME || ' ' || LASTNAME FROM EMP;  

  Q74)    What is the use of VALUE function?

  A74)     Avoid negative SQLCODEs by handling nulls and zeroes in computations.

Substitute a numeric value for any nulls used in computation.

  Q75)    What is UNION ,UNION ALL? - GS

  A75)     UNION                       eliminates duplicates

UNION ALL:             retains duplicates

Both these are used to combine the results of different SELECT statements.

  Q76)    Suppose I have five SQL SELECT statements connected by UNION/UNION ALL, how many times should I  

specify UNION to eliminate the duplicate rows? - GS

  A76)           Once.

  Q77)    What is the restriction on using UNION in embedded SQL?

  A77)     It has to be in a CURSOR.

  Q78)    In the WHERE clause what is BETWEEN and IN? - GS

  A78)     BETWEEN supplies a range of values while IN supplies a list of values.

  Q79)    Is BETWEEN inclusive of the range values specified? - GS

  A79)     Yes.

  Q80)    What is 'LIKE' used for in WHERE clause? What are the wildcard characters? - GS

  A80)     LIKE is used for partial string matches.  '%' ( for a string of any character ) and '_' (for any single character ) are the  

two wild card characters.

  Q81)    When do you use a LIKE statement?

  A81)     To do partial search e.g. to search employee by name, you need not specify the complete name; using LIKE, you can  

search for partial string matches.

  Q82)    What is the meaning of underscore ( '_' ) in the LIKE statement? - GS

  A82)     Match for any single character.

  Q83)    What do you accomplish by GROUP BY ... HAVING clause? - GS

  A83)     GROUP BY partitions the selected rows on the distinct values of the column on which you group by. HAVING selects  

GROUPs which match the criteria specified

  Q84)    Consider the employee table with column PROJECT nullable.  How can you get a list of employees who are not  

assigned to any project?

  A84)           SELECT EMPNO FROM EMP WHERE PROJECT IS NULL;

  Q85)    What is the result of this query if no rows are selected:

SELECT SUM(SALARY) FROM EMP WHERE QUAL='MSC';

  A85)     NULL

  Q86)    Why SELECT * is not preferred in embedded SQL programs?

For  three reasons:

If the table structure is changed (a field is added), the program will have to be modified

Program might retrieve the columns which it might not use, leading on I/O over head.

The chance of an index only scan is lost.

  Q87)    What are correlated subqueries? - GS

A subquery in which the inner ( nested ) query refers back to the table in the outer query. Correlated

subqueries must be evaluated for each qualified row of the outer query that is referred to.

  Q88)    What is a cursor? Why should it be used? - GS

Cursor is a programming device that allows the SELECT to find a set of rows but return them one at a time.

Cursor should be used because the host language can deal with only one row at a time.

  Q89)    How would you retrieve rows from a DB2 table in embedded SQL? - GS

Either by using the single row SELECT statements,or by using the CURSOR.

  Q90)    Apart from cursor, what other ways are available to you to retrieve a row from a table in embedded SQL? - GS

Single row SELECTs.

  Q91)    How do you specify and use a cursor in a COBOL program? - GS

Use DECLARE CURSOR statement either in working storage or in procedure division (before open cursor),

to specify the SELECT statement.  Then use OPEN, FETCH rows in a loop and finally CLOSE.

  Q92)    What happens when you say OPEN CURSOR?

If there is an ORDER BY clause, rows are fetched, sorted and made available for the FETCH statement. Other wise simply the cursor is placed on the first row.

  Q93)    Is DECLARE CURSOR executable?

No.

  Q94)    Can you have more than one cursor open at any one time in a program ? - GS

Yes.

  Q95)    When you COMMIT, is the cursor closed?

Yes.

  1.        What is SQLCA and SQLDA?

  2.        What is 2 phase commit?

DATABASE 2(DB2)

The questions and answers that follow are intended for those with a working knowledge of DB2 as a “self-test”.

  Q1)  What is DB2 (IBM Database 2)?

  A1)  DB2 is a subsystem of the MVS operating system. It is a Database Management System (DBMS) for that operating system.

  Q2)  What is an access path?

  A2)  The path that is used to get to data specified in SQL statements.

  Q3)  What is an alias?

  A3)  It is an alternate name that can be used in SQL statements to refer to a table or view in the same or remote DB2 subsystem.

  Q4)  Explain what a plan is?

  A4)  Plan is a DB2 object (produced during the bind process) that associates one or more database request modules with a plan name.

  Q5)  What is a DB2 bind?

  A5)  Bind is a process  that builds “access paths” to DB2 tables. A bind uses the Database Request Modules(s) (DBRM(s)) from the DB2 pre-compile step as input and produces an application plan. It also checks the user’s authority and validates the SQL statements in the DBRM(s).  

  Q6)  What information is used as input to the bind process?

  A6)  The database request module produced during the pre-compile. The SYSIBM.SYSSTMT table of the DB2 catalog.

  Q7)  What is meant by the attachment facility?

  A7)  The attachment facility is an interface between DB2 and TSO, IMS/VS, CICS, or batch address spaces. It allows application programs to access DB2.

  Q8)  What is meant by AUTO COMMIT?

  A8)  AUTO COMMIT is a SPUFI option that commits the effects of SQL statements automatically if they are successfully executed.

  Q9)  What is a base table?

  A9)  A base table is a real table -  a table that physically exists in that there are physical stored records.

  Q10)    What is the function of buffer manager?

  A10)           The buffer manager is the DB2 component responsible for physically transferring data between an external medium and (virtual) storage (performs the actual I/O operations). It minimizes the amount of physical I/O actually performed with sophisticated buffering techniques(i.e., read-ahead buffering and look-aside buffering).

  Q11)    What is a buffer pool?

  A11)           A buffer pool is main storage that is reserved to satisfy the buffering requirements for one or more tablespaces or indexes, and is made up of either 4K or 32K pages.

  Q12)    How many buffer pools are there in DB2?

  A12)           There are four buffer pools: BP0, BP1, BP2, and BP32.

  Q13)    On the create tablespace, what does the CLOSE parameter do?

  A13)           CLOSE physically closes the tablespace when no one is working on the object. DB2 (release 2.3) will logically close tablespaces.

  Q14)    What is a clustering index?

  A14)           It is a type of index that (1) locates table rows and (2) determines how rows are grouped together in the tablespace.

  Q15)    What will the COMMIT accomplish?

  A15)           COMMIT will allow data changes to be permanent. This then permits the data to be accessed by other units of work. When a COMMIT occurs, locks are freed so other applications can reference the just committed data.

  Q16)    What is meant by concurrency?

  A16)           Concurrency is what allows more than one DB2 application process to access the same data at essentially the same time. Problems may occur, such as lost updates, access to uncommitted data, and un-repeatable reads.

  Q17)    What is cursor stability?

  A17)           It is cursor stability that “tells” DB2 that database values read by this application are protected only while they are being used.   (Changed values are protected until this application reaches the commit point). As soon as a program moves from one row to another, other programs may read or the first row.

  Q18)    What is the function of the Data Manager?

  A18)           The Data Manager is a DB2 component that manager the physical databases. It invokes other system components, as necessary, to perform detailed functions such as locking, logging, and physical I/O operations (such as search, retrieval, update, and index maintenance).

  Q19)    What is a Database Request Module(DBRM)?

  A19)           A DBRM is a DB2 component created by the DB2 pre-compiler containing the SQL source statements extracted from the application program. DBRMs are input to the bind process.

  Q20)    What is a data page?

  A20)           A data page is a unit of retrievable data, either 4K or 32K (depending on how the table is defined), containing user or catalog information.

  Q21)    What are data types?

  A21)           They are attributes of columns, literals, and host variables. The data types are SMALLINT, INTEGER, FLOAT, DECIMAL, CHAR, VARCHAR, DATE and TIME.

  Q22)    What is Declaration Generator(DCLGEN)?

  A22)           DCLGEN is a facility that is used to generate SQL statements that describe a table or view. These table or view descriptions are then used to check the validity of other SQL statements at precompile time. The table or view declares are used by the DB2I utility DCLGEN to build a host language structure, which is used by the DB2 precompiler to verify that correct column names and data types have been specified in the SQL statement.

  Q23)    What does DSNDB07 database do?

  A23)           DSNDB07 is where DB2 does its sorting. It includes DB2’s sort work area and external storage.

  Q24)    What will the FREE command do to  a  plan?

  A24)           It will drop(delete) that existing plan.

  Q25)    What is a host variable?

  A25)           This is a data item that is used in an SQL statement to receive a value or to supply a value. It must be preceded by a colon (:) to tell DB2 that the variable is not a column name.

  Q26)    What will the DB2 optimizer do?

  A26)           The optimizer is a DB2 component that processes SQL statements and selects the access paths.

  Q27)    What is a page?

  A27)           This is the unit of storage within a table space or indexspace that is accessed by DB2.

  Q28)    What is pagespace?

  A28)           Pagespace refers to either to an unpartitioned table, to an index space, or to a single partition of a partitioned table of index space.

  Q29)    What is a predicate?

  A29)           A predicate is an element of a search condition that expresses or implies a comparison operation.

  Q30)    What is a recovery log?

  A30)           A recovery log is a collection of records that describes the sequence of events that occur in DB2. The information is needed for recovery in the event of a failure during execution.

  Q31)    What is a Resource Control Table(RCT)? Describe its characteristics.

  A31)           The RCT is a table that is defined to a DB2/CICS region. It contains control characteristics which are assembled via the DSNCRCT macros. The RCT matches the CICS transaction ID to its associated DB2 authorization ID  and plan ID(CICS attachment facility).

  Q32)    Where are plans stored?

  A32)           Each plan is defined uniquely in the SYSIBM.SYSPLANS table to correspond to the transaction (s) that are to execute that plan.

  Q33)    What is meant by repeatable read?

  A33)           When an application program executes with repeatable read protection, rows referenced by the program can’t be changed by  other programs until the program reaches a commit point.

  Q34)    Describe what a storage group(STOGROUP) is?

  A34)           A STOGROUP is a named collection of DASD volumes to be used by tablespaces and index spaces of databases. The volumes of STOGROUP must be of the same device type.

  Q35)    How would you move a tablespace (using STOGROUP) to a different DASD volume allocated to that tablespace?

  A35)           If the tablespace used is only allocated to that STOGROUP:

                - ALTER STOGROUP - add volume (new) delete volume(old)

  -          REORG TABLESPACE or RECOVER TABLESPACE

            Create a new STOGROUP that points to the new volume. ALTER the tablespace and REORG or RECOVER the

            tablespace.

  Q36)    What is the format (internal layout) of “TIMESTAMP”?

  A36)           This is a seven part value that consists of a date (yymmdd) and time(hhmmss and microseconds).

  Q37)    What is meant by a unit of recovery?

  A37)           This is a sequence of operations within a unit of work(i.e., work done between commit points).

  Q38)    Can DASD types assigned to storage groups be intermixed(i.e., 3350s and 3380s)?

  A38)           No

  Q39)    What are the three types of page locks that can be held?

  A39)           Exclusive, update, and share.

  Q40)    Can DB2 be accessed by TSO users? If yes, which command is used to invoke DB2?

  A40)           DB2 can be invoked by TSO users by using the DSN RUN command.

  Q41)    How are write I/Os from the buffer pool executed?

  A41)           Asynchronously.

  Q42)    What is a DB2 catalog?

  A42)           The DB2 catalog is a set of tables that contain information about all of the DB2 objects(tables, views, plans etc.).

  Q43)    In which column of which DB2 catalog would you find the length of the rows for all tables?

  A43)           In the RECLENGTH column of SYSIBM.SYSTABLES

  Q44)    What information is held in SYSIBM.SYSCOPY?

  A44)           The SYSIBM.SYSCOPY table contains information about image copies made of the tablespaces.

  Q45)    What information is contained in a SYSCOPY entry?

  A45)           Included is the name of the database, the table space name, and the image copy type(full or incremental etc.,) as well as the date and time each copy was made.

  Q46)    What information can you find in SYSIBM.SYSLINKS table?

  A46)           The SYSIBM.SYSLINKS table contains information about the links between tables created by referential constraints.

  Q47)    Where would you find information about the type of database authority held by the user?

  A47)           SYSIBM.SYSDBAUTH.

  Q48)    Where could you look if you had a question about whether a column has been defined as an index?

  A48)           This information can be found in SYSIBM.SYSINDEXES.

  Q49)    Once you create a view, where would information about the view be stored?

  A49)           When a view is created, system information about the view is stored in SYSIBM.SYSVIEWS.

  Q50)    What is the SQL Communications Area and what are some of its key fields?  

  A50)           It is a data structure that must be included in any host-language program using SQL.  It is used to pass feedback about the sql operations to the program.  Fields are return codes, error messages, handling codes and warnings.  

  Q51)    What is DCLGEN?  

  A51)           DCLGEN stands for declarations generator;  it is a facility to generate DB2 sql data structures in COBOL or PL/I programs.  

  Q52)    How do you leave the cursor open after issuing a COMMIT?  (for DB2 2.3 or above only)

  A52)           Use WITH HOLD option in DECLARE CURSOR statement.  But, it has not effect in psuedo-conversational CICS programs.

  Q53)    Give the COBOL definition of a VARCHAR field.

  A53)           A VARCHAR column REMARKS would be defined as follows:

...

10 REMARKS.

              49 REMARKS-LEN    PIC S9(4) USAGE COMP.

              49 REMARKS-TEXT   PIC X(1920).

  Q54)    What is the physical storage length of each of the following DB2 data types: DATE, TIME, TIMESTAMP?

  A54)           DATE:                    4bytes

TIME:                         3bytes

TIMESTAMP:          10bytes

  Q55)    What is the COBOL picture clause of the following DB2 data types:  DATE, TIME, TIMESTAMP?

  A55)           DATE:                    PIC X(10)

TIME :                        PIC X(08)

TIMESTAMP:          PIC X(26)

  Q56)    What is the COBOL picture clause for a DB2 column defined as DECIMAL(11,2)? - GS

  A56)           PIC S9(9)V99 COMP-3.

Note: In DECIMAL(11,2), 11 indicates the size of the data type and 2 indicates the precision.

  Q57)    What is DCLGEN ? - GS

  A57)           DeCLarations GENerator: used to create the host language copy books for the table definitions. Also creates the DECLARE table.

  Q58)    What are the contents of a DCLGEN? - GS

  A58)           EXEC SQL DECLARE TABLE statement which gives the layout of the table/view in terms of DB2 datatypes.

A host language copy book that gives the host variable definitions for the column names.

  Q59)    Is it mandatory to use DCLGEN? If not, why would you use it at all? - GS

  A59)           It is not mandatory to use DCLGEN. Using DCLGEN, helps detect wrongly spelt column names etc. during the pre-compile stage itself (because of the DECLARE TABLE ).  DCLGEN being a tool, would generate accurate host variable definitions for the table reducing chances of error.

  Q60)    Is DECLARE TABLE in DCLGEN necessary? Why it used?

  A60)           It not necessary to have DECLARE TABLE statement in DCLGEN.  This is used by the pre-compiler to validate the table-name, view-name, column name etc., during pre-compile.

  Q61)    Will precompile of an DB2-COBOL program bomb, if DB2 is down?

  A61)           No.  Because the precompiler does not refer to the DB2 catalogue tables.

  Q62)    How is a typical DB2 batch program executed ?  

  A62)           There are two methods of executing a DB2-batch program  

1. Use DSN utility to run a DB2 batch program from native TSO.  An example is shown:

DSN SYSTEM(DSP3)

    RUN PROGRAM(EDD470BD) PLAN(EDD470BD) LIB('EDGS01T.OBJ.LOADLIB')

END

2. Use IKJEFT01 utility program to run the above DSN command in a JCL.

  Q63)    Assuming that a site's standard is that pgm name = plan name, what is the easiest way to find out which  

programs are affected by change in a table's structure?

  A63)           Query the catalogue tables SYSPLANDEP and SYSPACKDEP.

  Q64)    Name some fields from SQLCA.

  A64)           SQLCODE, SQLERRM, SQLERRD

  Q65)    How can you quickly find out the number of rows updated after an update statement?

  A65)           Check the value stored in SQLERRD(3).

  Q66)    What is EXPLAIN? - GS

  A66)           EXPLAIN is used to display the access path as determined by the optimizer for a SQL statement.  It can be used in SPUFI (for single SQL statement) or in BIND step (for embedded SQL).  The results of EXPLAIN is stored in U.PLAN_TABLE where U is the authorization id of the user

  Q67)    What do you need to do before you do EXPLAIN?

  A67)           Make sure that the PLAN_TABLE is created under the AUTHID.

  Q68)    Where is the output of EXPLAIN stored? - GS

  A68)           In USERID.PLAN_TABLE   

  Q69)    EXPLAIN has output with MATCHCOLS = 0.  What does it mean? - GS

  A69)           A nonmatching index scan if ACCESSTYPE = I.

  Q70)    How do you do the EXPLAIN of a dynamic SQL statement?

  A70)           There are two methods to achieve this:

1. Use SPUFI or QMF to EXPLAIN the dynamic SQL statement

2. Include EXPLAIN command in the embedded dynamic SQL statements

  Q71)    How do you simulate the EXPLAIN of an embedded SQL statement in SPUFI/QMF? Give an example with a host variable in WHERE clause)

  A71)           Use a question mark in place of a host variable (or an unknown value). For instance,  

SELECT EMP_NAME FROM EMP WHERE EMP_SALARY > ?

  Q72)    What are the isolation levels possible ? - GS

  A72)           CS:          Cursor Stability

RR:              Repeatable Read

  Q73)    What is the difference between CS and RR isolation levels?

  A73)           CS:          Releases the lock on a page after use

RR:             Retains all locks acquired till end of transaction

  Q74)    When do you specify the isolation level? How?

  A74)           During the BIND process(ISOLATION LEVEL is a parameter for the bind process).  ISOLATION ( CS/RR )...

  Q75)    I use CS and update a page.  Will the lock be released after I am done with that page?

  A75)           No.

  Q76)    What are the various locking levels available?

  A76)           PAGE, TABLE, TABLESPACE

  Q77)    How does DB2 determine what lock-size to use?

  A77)           There are three methods to determine the lock-size.  They are:

1. Based on the lock-size given while creating the tablespace

2. Programmer can direct the DB2 what lock-size to use

3. If lock-size ANY is specified, DB2 usually choses a lock-size of PAGE

  Q78)    What are the disadvantages of PAGE level lock?

  A78)           High resource utilization if large updates are to be done

  Q79)    What is lock escalation?

  A79)           Promoting a PAGE lock-size to table or tablespace lock-size when a transaction has aquired more locks than specified in NUMLKTS.  Locks should be taken on objects in single tablespace for escalation to occur.

  Q80)    What are the various locks available?

  A80)           SHARE, EXCLUSIVE, UPDATE

  Q81)    Can I use LOCK TABLE on a view?

  A81)           No.  To lock a view, take lock on the underlying tables.

  Q82)    What is ALTER ? - GS

  A82)           SQL command used to change the definition of DB2 objects.

  Q83)    What is a DBRM, PLAN ?

  A83)           DBRM: Data Base Request Module, has the SQL statements extracted from the host language program by  the pre-compiler. PLAN: A result of the BIND process.  It has the executable code for the SQL statements in the DBRM.

  Q84)    What is ACQUIRE/RELEASE in BIND?

  A84)           Determine the point at which DB2 acquires or releases locks against table and tablespaces, including intent locks.

  Q85)    What else is there in the PLAN apart from the access path? - GS

  A85)           PLAN has the executable code for the SQL statements in the host program

  Q86)    What happens to the PLAN if index used by it is dropped?

  A86)           Plan is marked as invalid. The next time the plan is accessed, it is rebound.

  Q87)    What are PACKAGES ? - GS

  A87)           They contain executable code for SQL statements for one DBRM.

  Q88)    What are the advantages of using a PACKAGE?

  A88)           The advantages of using PACKAGE are:

1. Avoid having to bind a large number of DBRM members into a plan

2. Avoid cost of a large bind

3. Avoid the entire transaction being unavailable during bind and automatic rebind of a plan

4. Minimize fallback complexities if changes result in an error.

  Q89)    What is a collection?

  A89)           A user defined name that is the anchor for packages.  It has not physical existence.  Main usage is to group packages.

  Q90)    In SPUFI suppose you want to select maximum of 1000 rows, but the select returns only 200 rows. What are the 2 SQLCODEs that are returned? - GS

  A90)           +100 (for successful completion of the query), 0 (for successful COMMIT  if AUTOCOMMIT is set to Yes).

  Q91)    How would you print the output of an SQL statement from SPUFI? - GS

  A91)           Print the output dataset.

  Q92)    Lot of updates have been done on a table due to which indexes have gone haywire.  What do you do?

  A92)           Looks like index page split has occurred.  DO a REORG of the indexes.

  Q93)    What is dynamic SQL? - GS

  A93)           Dynamic SQL is a SQL statement created at program execution time.