Control statements

There are several control statements for logical flow and decision making in the body of a procedure, trigger, or user-defined function, or in a batch. Available control statements include:

BEGIN [ ATOMIC ]
   Statement-list
END

IF condition THEN
   Statement-list
ELSEIF condition THEN
   Statement-list
ELSE
   Statement-list
END IF

CASE expression
WHEN value THEN
   Statement-list
WHEN value THEN
   Statement-list
ELSE
   Statement-list
END CASE

WHILE condition LOOP
   Statement-list
END LOOP

FOR loop-name
   AS cursor-name CURSOR FOR
   select-statement
DO
   Statement-list
END FOR

LEAVE label

CALL procname( arg, ... )

• Compound statements
  A compound statement starts with the keyword BEGIN and concludes with the keyword END. The body of a procedure or trigger is a compound statement. Compound statements can also be used in batches. Compound statements can be nested, and combined with other control statements to define execution flow in procedures and triggers or in batches.
• Declarations in compound statements
  Local declarations in a compound statement immediately follow the BEGIN keyword. These local declarations exist only within the compound statement. Within a compound statement you can declare:
• Atomic compound statements
  An atomic statement is a statement that is executed completely or not at all. For example, an UPDATE statement that updates thousands of rows might encounter an error after updating many rows. If the statement does not complete, all changed rows revert back to their original state. The UPDATE statement is atomic.