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CHAPTER 6 Using Procedures and Batches
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DBISQL and batches
A list of semicolon-separated statements, such as the above, is parsed by
DBISQL before it is sent to the server. In this case, DBISQL sends each
statement individually to the server, not as a batch. Unless you have such
parsing code in your application, the statements would be sent and treated as a
batch. Putting a
BEGIN and END around a set of statements causes DBISQL to
treat them as a batch.
Many statements used in procedures can also be used in batches. You can use
control statements (
CASE, IF, LOOP, and so on), including compound
statements (
BEGIN and END), in batches. Compound statements can include
declarations of variables, exceptions, temporary tables, or cursors inside the
compound statement.
The following batch creates a table only if a table of that name does not already
exist:
BEGIN
IF NOT EXISTS (
SELECT * FROM SYSTABLE
WHERE table_name = ’t1’ ) THEN
CREATE TABLE t1 (
firstcol INT PRIMARY KEY,
secondcol CHAR( 30 )
) ;
ELSE
MESSAGE ’Table t1 already exists’ ;
END IF
END
If you run this batch twice from DBISQL, it creates the table the first time you
run it. The next time you run it, it prints the message in the server log file on
Unix or on the server message window on Windows NT.
Control statements
There are a number of control statements for logical flow and decision making
in the body of the procedure or in a batch. The following is a list of control
statements available.