Thread: Dynamic SQL

Hi all,
    I'd like to write a function that would allow me to verify some attributes on a table so that I could give a meaningful error message...

I've been playing with passing in to a plpgsql function the following things.

CREATE OR REPLACE FUNCTION fn_verifyObject( VARCHAR, VARCHAR, BIGINT, VARCHAR ) RETURNS BOOLEAN AS'
declare
    tableName ALIAS FOR $1;
    idColumn   ALIAS FOR $2;
    objectId     ALIAS FOR $3;
    errorMsg    ALIAS FOR $4;

    recCheckObject RECORD;
    constructedSql TEXT := '''';
begin
     constructedSql = ''SELECT INTO recCheckObject * FROM '' || tableName || '' WHERE '' || idColumn || '' = '' || objectId;
     EXECUTE constructedSql;
    
-- this is where I expect the command to run, as though I had typed it in and thus populate, or fail to populate the record recCheckObject.
    IF NOT FOUND THEN
            RAISE EXCEPTION ''VERIFY OBJECT FAILED FOR:%:%:%:%'', tableName, idColumn, objectId, errorMsg;
    END IF;

    --found something, therefore success.
    RETURN TRUE;
END;'language'plpgsql';

CREATE TABLE testcode(
        id    BIGINT    NOT NULL,
        CONSTRAINT pk_testcode PRIMARY KEY( id )
);

INSERT INTO testcode VALUES ( 1 );

SELECT fn_verifyObject( 'testcode', 'id', 1, 'VERFIY_TEST_CODE' );


However, when you try and run this it's like the SELECT INTO <record> is failing to pickup the reference to the declared variable?

I get...ERROR:  syntax error at or near "INTO" at character 8
CONTEXT:  PL/pgSQL function "fn_verifyobject" line 11 at execute statement

Can anybody help by telling me how to either quote or execute this constructed SQL correctly.

Regards.
    Hadley


   

Hadley Willan wrote:
> Hi all,
>     I'd like to write a function that would allow me to verify some
> attributes on a table so that I could give a meaningful error message...
>

>      constructedSql = ''SELECT INTO recCheckObject * FROM '' ||
> tableName || '' WHERE '' || idColumn || '' = '' || objectId;
>      EXECUTE constructedSql;

> However, when you try and run this it's like the SELECT INTO <record> is
> failing to pickup the reference to the declared variable?

Sounds likely, and (without testing anything) I wouldn't expect it to work.

Indeed, checking the manuals: plpgsql / basic statements (37.6.4)
"The results from SELECT commands are discarded by EXECUTE, and SELECT
INTO is not currently supported within EXECUTE. There are two ways to
extract a result from a dynamically-created SELECT: one is to use the
FOR-IN-EXECUTE loop form described in Section 37.7.4, and the other is
to use a cursor with OPEN-FOR-EXECUTE, as described in Section 37.8.2."

There's your solution - you need to use the FOR rec IN ... looping
construct.

--
   Richard Huxton
   Archonet Ltd