I've written a stored procedure function to get a name from a table. The trouble is that I want the table name to be passed in as a parameter (there are several different tables I need to use this function with):
DELIMITER $$
CREATE DEFINER=`root`@`localhost` FUNCTION `getName`(tableName VARCHAR(50), myId INT(11)) RETURNS VARCHAR(50)
begin
DECLARE myName VARCHAR(50);
SELECT
'name' INTO myName
FROM
tableName
WHERE
id=myId;
RETURN myName;
end
This method has an error because it uses the variable name "tableName" instead of the actual value of the variable.
I can work around this problem in a procedure by using a CONCAT
like this:
SET @GetName = CONCAT("
SELECT
'name'
FROM
",tableName,"
WHERE
id=",myId,";
");
PREPARE stmt FROM @GetName;
EXECUTE stmt;
...but, when I try to do this in a function I get a message saying:
Dynamic SQL is not allowed in stored function or trigger
I tried to use a procedure instead, but I couldn't get it to just return a value, like a function does.
So, can anyone see a way to get around this problem. It seems incredibly basic really.
If you want to buld a SQL statement using identifiers, then you need to use prepared statements; but prepared statements cannot be used in functions. So, you can create a stored procedure with OUT parameter -
CREATE PROCEDURE getName
(IN tableName VARCHAR(50), IN myId INT(11), OUT myName VARCHAR(50))
BEGIN
SET @GetName =
CONCAT('SELECT name INTO @var1 FROM ', tableName, ' WHERE id=', myId);
PREPARE stmt FROM @GetName;
EXECUTE stmt;
SET myName = @var1;
END
Using example -
SET @tableName = 'tbl';
SET @myId = 1005;
SET @name = NULL;
CALL getName(@tableName, @myId, @name);
SELECT @name;
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