To find the number of rows in a DB2 table, the user has to use SELECT COUNT (*) on the DB2 query.
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To eliminate the duplicate values from DB2 SELECT, the user has to use SELECT DISTINCT in the DB2 query.
‘Aggregate’ functions are built-in mathematical tools that are used in the DB2 SELECT clause.
Yes! It is possible using MAX on a CHAR column.
The reason for the statement generating an inaccurate outcome is that SALARY has not been declared to have NULL values and, at the same time, the employees whose salary is not known are also counted.
Below is the statement that can be used to concatenate the first and last names to display full names:
FIRSTNAME II ** II LASTNAME FROM EMP
We can perform two tasks using the ‘value’ function:
Both UNION and UNION ALL are used to combine the results generated by multiple SELECT statements.
While using UNION in Embedded SQL, it has to be in a CURSOR.
BETWEEN would supply a range of values, whereas IN would provide a list of values. BETWEEN is always inclusive of the range values specified.
The LIKE statement is used to conduct partial searches such as the search of employees by name. It is not necessary to indicate the complete name, partial string matches would do.
SELECT is not preferred in Embedded SQL programs for three reasons. First, if the table structure is changed by the addition or deletion of a field and the program is modified, then using SELECT might retrieve the columns that the user may not use. This would lead to Input-Output overhead and the chances of index-only scan are also eliminated.
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A CURSOR is a programming device that helps the SELECT statement find out a set of rows but displays them one at a time. This is because the host language can deal with only one row at a time.
Rows from a DB2 table in Embedded SQL can be retrieved using the single-row SELECT statement. Another way is by using the CURSOR statement. However, the first process is the preferred one.
In the simple OPEN CURSOR statement, the CURSOR is placed on the first row of a table. On the other hand, when the ORDER BY clause is added, rows would be fetched, sorted, and would be available for the FETCH statement.
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Yes! The user can have more than one cursor open for any program.
The VARCHAR column REMARKS would be defined as follows:
The physical storage length of DATE is 4 bytes, TIME is 3 bytes, and TIMESTAMP is 10 bytes.
DCLGEN refers to Declaration Generator that is used to create the host language copy books for the table definitions. It also creates the DECLARE table.
DCLGEN has the EXEC SQL DECLARE TABLE statement that gives the layout of a table/view in terms of DB2 data types. It can also be defined as the host language copy book giving the host variable definitions for column names.
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Major fields in SQLCA are SQLCODE, SQLERRM, and SQLERRD.
EXPLAIN is used for displaying the access path as determined by the optimizer for SQL statements. It can also be used in the case of SPUFI for single SQL statements or in the BIND step for Embedded SQL.
Users can use SPUFI or QMF statements to perform EXPLAIN for Dynamic SQL statements. They can also include the EXPLAIN command in the Embedded Dynamic SQL statements.
Two isolation levels are possible: One is Cursor Stability and the other is Repeatable Read denoted as CS and RR, respectively.
CS would release the lock on the page after its use. RR would retain all the locks acquired till the end of a transaction.
Lock escalation is the process of promoting page lock sizes to table or table space lock size when the transaction has acquired more locks than the ones specified in NUMLKTS. Locks have to be taken on objects in a single table space for escalations to take place.
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There are three different types of locks: SHARE, EXCLUSIVE, and UPDATE.
ALTER is the SQL command used to change the definition of DB2 objects.
DBRM denotes Database Request Module. It has the SQL statements that are extracted from the host language program obtained by the pre-compiler.
PLAN is the result of the BIND process and has executable code for SQL statements in DBRM.
ACQUIRE/RELEASE in BIND determines the point at which DB2 either acquires or releases locks against the table and the table spaces. This includes the intent locks.
PACKAGES contain executable codes for SQL statements in respect of one DBRM.
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When used, PACKAGES help avoid binding of large numbers of DBRM members in one plan. They also dispense with the cost of large BIND and avoid the entire transactions making them unavailable during BIND and automatic REBIND of the plan. Another advantage is that they minimize the fallback complexities when changes result in an error.
A collection is a user-defined name that works as the anchor for packages but has no physical existence. It is used for the grouping of packages.
Dynamic SQL is the SQL statement created at the time of the execution of a program.
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