How to execute PostgreSQL RAISE command dynamically - postgresql

Question

How to raise error from PostgreSQL SQL statement if some condition is met?
I tried code below but got error.
CREATE OR REPLACE FUNCTION "exec"(text)
RETURNS text AS
$BODY$
BEGIN
EXECUTE $1;
RETURN $1;
END;
$BODY$
LANGUAGE plpgsql VOLATILE;
-- ERROR: syntax error at or near "raise"
-- LINE 1: raise 'test'
SELECT exec('raise ''test'' ') WHERE TRUE
In real application TRUE is replaced by some condition.
Update
I tried to extend answer to pass exception message parameters.
Tried code below but got syntax error.
How to pass message parameters ?
CREATE OR REPLACE FUNCTION exec(text, variadic )
RETURNS void LANGUAGE plpgsql AS
$BODY$
BEGIN
RAISE EXCEPTION $1, $2;
END;
$BODY$;
SELECT exec('Exception Param1=% Param2=%', 'param1', 2 );

Answer 1

You cannot call RAISE dynamically (with EXECUTE) in PL/pgSQL - that only works for SQL statements, and RAISE is a PL/pgSQL command.
Use this simple function instead:
CREATE OR REPLACE FUNCTION f_raise(text)
RETURNS void
LANGUAGE plpgsql AS
$func$
BEGIN
RAISE EXCEPTION '%', $1;
END
$func$;
Call:
SELECT f_raise('My message is empty!');
Related:
Generate an exception with a Context
Additional answer to comment
CREATE OR REPLACE FUNCTION f_raise1(VARIADIC text[])
RETURNS void
LANGUAGE plpgsql AS
$func$
BEGIN
RAISE EXCEPTION 'Reading % % %!', $1[1], $1[2], $1[3];
END
$func$;
Call:
SELECT f_raise1('the','manual','educates');
VARIADIC is not a data type, but an argument mode.
Elements have to be handled like any other array element.
To use multiple variables in a RAISE statement, put multiple % into the message text.
The above example will fail if no $3 is passed. You'd have to assemble a string from the variable number of input elements. Example:
CREATE OR REPLACE FUNCTION f_raise2(VARIADIC _arr text[])
RETURNS void
LANGUAGE plpgsql AS
$func$
DECLARE
_msg text := array_to_string(_arr, ' and '); -- simple string construction
BEGIN
RAISE EXCEPTION 'Reading %!', _msg;
END
$func$;
Call:
SELECT f_raise2('the','manual','educates');
I doubt you need a VARIADIC parameter for this at all. Read the manual here.
Instead, define all parameters, maybe add defaults:
CREATE OR REPLACE FUNCTION f_raise3(_param1 text = ''
, _param2 text = ''
, _param3 text = 'educates')
RETURNS void
LANGUAGE plpgsql AS
$func$
BEGIN
RAISE EXCEPTION 'Reading % % %!', $1, $2, $3;
END
$func$;
Call:
SELECT f_raise3('the','manual','educates');
Or:
SELECT f_raise3(); -- defaults kick in