NexusDB Guide > SQL Reference > SQL Statements > Control Statements

NexusDB V3 Manual

IF statement

NexusDB Manual V3 > SQL Reference > SQL Statements > Control Statements

Specify a conditional execution.

Syntax

<if statement> ::=

IF <search condition>

[ <if statement elseif clause>... ]

[ <if statement else clause> ]

END IF

<if statement elseif clause> ::= ELSEIF <search condition> THEN <SQL statement list>

Usage

The IF statement is used to specify a conditional execution of one or more SQL statements, and is similar in functionality to conditional IF statements found in traditional programming languages.

Notes

§	The optional ELSEIF clause is used to specify additional conditions with separate statement blocks, and is a convenient shorthand for nesting multiple IF..THEN statements.

§	Only the statements contained in the first IF or ELSEIF clause with a condition that evaluates to true are executed.

§	An optional ELSE clause can be specified to execute one or more statements if none of the preceding conditions were true.

Examples

1)	The following example shows the IF statement used in the body of a trigger definition:

DROP TRIGGER IF EXISTS enrolls_changes;

CREATE TRIGGER enrolls_changes

AFTER INSERT, DELETE, UPDATE ON enrolls

REFERENCING OLD AS o NEW AS n

BEGIN

IF INSERTING THEN

INSERT INTO enrolls_log ( action, n1, n2, n3, n4, stamp )

VALUES ( 'Insert', n.courseID, n.sectionID, n.studentID, n.grade, CURRENT_TIMESTAMP );

ELSEIF UPDATING THEN

INSERT INTO enrolls_log ( action, o1, n1, o2, n2, o3, n3, o4, n4, stamp )

VALUES ('Update', o.courseID, n.courseID, o.sectionID, n.sectionID,

o.studentID, n.studentID, o.grade, n.grade, CURRENT_TIMESTAMP );

ELSEIF DELETING THEN

INSERT INTO enrolls_log ( action, o1, o2, o3, o4, stamp )

VALUES ( 'Delete', o.courseID, o.sectionID, o.studentID, o.grade, CURRENT_TIMESTAMP );

ELSE

SIGNAL 'An unknown trigger event was fired.';

END IF;

END

Conformance

SQL:2003 standard

SQL/PSM Feature P002-07 "IF statement"

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