Introduction to batches

User's Guide
PART 1. Working with Databases
CHAPTER 10. Using Procedures, Triggers, and Batches

Introduction to batches

A simple batch consists of a set of SQL statements, separated by semicolons. For example, the following set of statements form a batch, which creates an Eastern Sales department and transfers all sales reps from Massachusetts to that department.

INSERT
INTO department ( dept_id, dept_name )
VALUES ( 220, 'Eastern Sales' ) ;

UPDATE employee
SET dept_id = 220
WHERE dept_id = 200
AND state = 'MA' ;

COMMIT ;

You can include this set of statements in an application and execute them together.

Interactive SQL and batches
A list of semicolon-separated statements, such as the above, is parsed by Interactive SQL before it is sent to the server. In this case, Interactive SQL 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 Interactive SQL to treat them as a batch.

Many statements used in procedures and triggers 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 Interactive SQL, it creates the table the first time you run it, and prints the message on the server message window the next time you run it.