有没有办法将 MySQL 中存储过程中准备好的语句返回的值存储在变量中？

Question

    DELIMITER  $$
    CREATE PROCEDURE prepared_return_value(IN columnName varchar(20), IN tableName varchar(20), IN rowIndex varchar(10))
    BEGIN
    SET @columnName = '';
    SET @columnName = CONCAT('Select distinct ',columnName ,' from ', tableName, ' LIMIT ', rowIndex, ',', '1', ';');
    -- SELECT @columnName;
    PREPARE stmt FROM @columnName;
    EXECUTE stmt;
    END $$
    DELIMITER ;

So, i'm trying to dynamic pivoting a table using prepared statements to return the unique value of the rows and use it to alter a table. But for that, i need to be able to store the returned row value, so i can use it in another prepared statement as the column name. Apparently i can't store the value from the execution of prepared statement neither from a procedure. I've tried lot of things by know, but none seemed to work, só... any hint on that?

Answer 1

The Varoable is session bound, so you can be used after the procedure has run.

SELECT @columnName

direct after the running outside if the procedure.

another option s to use an OUT Parameter besides the IN

Ypu would run

CALL return_value(columnName, tableName, rowIndex, @columnName)

And the crete procedure wil look like

CREATE PROCEDURE prepared_return_value(IN columnName varchar(20), IN tableName varchar(20), IN rowIndex varchar(10), OUT myoutput TEXT

Still what you are doing is highly problematic as it could be used for sql injection, so you should white list colu,nname an Tablename