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Stored Procedure to calculate sum

Posted on 2006-07-10
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Last Modified: 2008-01-16
hi,

i am having trouble writing a stored function in MySQL 5 that will return the sum of a series of values. i wrote this so far

CREATE FUNCTION `Max_Peso`(IN tbl CHAR(64), IN col CHAR(64), OUT s INT) RETURNS INT
    READS SQL DATA
    SQL SECURITY INVOKER
    COMMENT 'Sums all the maximum \'pesos\' grouped by category'
BEGIN
SET @s = CONCAT('SELECT SUM(MAX(' , col , ')) FROM ' , tbl, ' GROUP BY categoria');
PREPARE stmt FROM @s;
EXECUTE stmt;

RETURN s;
END;


but this is not working i get an error.
please help
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Question by:newyuppie
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6 Comments
 
LVL 33

Expert Comment

by:snoyes_jw
ID: 17076066
Functions do not have in/out parameters.  If you intend to make this a function, drop the "IN" from the parameter list, and do not include the 's' parameter.  If you intend to make this a procedure, change "FUNCTION" to "PROCEDURE" and adjust the "return" accordingly.

Dynamic SQL is not allowed in stored functions.
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LVL 13

Author Comment

by:newyuppie
ID: 17076178
thanks for the clarification. i now have this:

CREATE PROCEDURE `gr`(IN col VARCHAR, IN tbl VARCHAR)
    READS SQL DATA
    SQL SECURITY INVOKER
BEGIN
SET @s = CONCAT('SELECT SUM(MAX(' , col , ')) FROM ' , tbl, ' GROUP BY categoria');
PREPARE stmt FROM @s;
EXECUTE stmt;
END


and still get error. could you help me construct this procedure?
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LVL 33

Expert Comment

by:snoyes_jw
ID: 17076239
varchar fields must have a length specified, such as varchar(64)
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LVL 13

Author Comment

by:newyuppie
ID: 17076250
ok UPDATE


i was missing in the IN col VARCHAR, missing to put (255) in the end. it now works, code is like this:
CREATE PROCEDURE `gr`(IN PCol VARCHAR(255), IN Ptbl VARCHAR(255))
    READS SQL DATA
    SQL SECURITY INVOKER
BEGIN
SET @s = CONCAT('SELECT MAX(' , PCol , ') FROM ' , PTbl, ' GROUP BY categoria');
PREPARE stmt FROM @s;
EXECUTE stmt;
DROP PREPARE stmt;
END


i get a list of the MAX values for each category. how do i SUM all these, and return the single summed value?
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LVL 33

Accepted Solution

by:
snoyes_jw earned 500 total points
ID: 17076343
make your query this:
SET @s = CONCAT('SELECT SUM(theColumn) INTO s FROM (SELECT MAX(', PCol, ') AS theColumn FROM ', Ptbl, ' GROUP BY categoria) AS theValues');

and add your OUT s INT back in.
0
 
LVL 13

Author Comment

by:newyuppie
ID: 17079326
thanks

i removed the INTO s and excluded the OUT s INT from the declaration (because i kept getting errors). without these things, it works and returns a single row with the appropiate number,

thanks for your help!
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