How to write a mysql function with dynamic table name? - mysql

Question

I'm trying to write a my sql function doing the following things:
1- get the table name used in join as a parameter.
but I get mysql syntax error
1064 - You have an error in your SQL syntax; check the manual that corresponds to
your MySQL server version for the right syntax to use near 'table DETERMINISTIC
BEGIN select `r`.`id` AS `id`, (case ' at line 2
This is my query
DELIMITER $$
CREATE FUNCTION getTranslation (tablename varchar(50),entity varchar(20),itemid int,lang char(3))
RETURNS table
DETERMINISTIC
BEGIN
select
`r`.`id` AS `id`,
(case
when isnull(`t`.`descr`) then `r`.`descr_ml`
else `t`.`descr`
end) AS `descr`
from
(tablename `r`
left join `g001_translation` `t` ON ((`t`.`item_id` = `r`.`id`)))
END$$
DELIMITER ;
I the select part works fine with static table name by the way.

Answer 1

First up as mentioned by #eggyal this isn't the best way to go about things. But it can be done by using prepared statements. I.e.
DROP PROCEDURE IF EXISTS `exampleOfPrepareStatement`;
CREATE DEFINER = `user`#`%` PROCEDURE `exampleOfPrepareStatement`(inTableName VARCHAR(100))
MODIFIES SQL DATA
SQL SECURITY INVOKER
BEGIN
SET #hr1 = CONCAT('
INSERT INTO `',inTableName,'` (
-- fields (can use parameters same as table name if needed)
)
-- either VALUES () or SELECT here
');
-- Prepare, execute, deallocate
PREPARE hrStmt1 FROM #hr1;
EXECUTE hrStmt1;
DEALLOCATE PREPARE hrStmt1;
END;
You can of course add in field names etc. as needed, or use a SELECT or UPDATE etc. This is not ideal, but will do what you are looking for.
I have had to use this in some places before where the same maintenance is being performed on multiple tables which have different field names ( / table names ) and so instead of writing the same function 20 times, instead I use this type of stored procedure which can then be called to do the indexing etc.
As also mentioned by #eggyal , while this may do as you ask, it might not do as you need. If you can provide more information then you may get a better solution.

Answer 2

Give this a try
SET #ex = CONCAT('select `r`.`id` AS `id`,(case when isnull(`t`.`descr`) then `r`.`descr_ml` else `t`.`descr` end) AS `descr` from (',tablename,' `r` left join `g001_translation` `t` ON ((`t`.`item_id` = `r`.`id`)));');
PREPARE stmt FROM #ex;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
You will notice that ',tablename,' will use the parameter passed.