MySQL Pass table name to cursor select

问题

I want the procedure to take parameter answertable and partid in the select statement, but when i call it it doesn't replace the parameter answertable with the value

the call call updateTotalScores('quiz_participation', 'quiz_answer', 1)

returns the error: 1146 - Table 'quizdb.answertable' doesn't exist

passing the id works, but passing the table name doesn't so how do i pass the table name to the select in

DECLARE cur1 CURSOR FOR SELECT SUM(`score`), SUM(`maxscore`) FROM answertable WHERE `idParticipation`=partid;

entire procedure:

DELIMITER $$
CREATE PROCEDURE updateTotalScores(IN participationtable CHAR(64), IN answertable CHAR(64), IN partid INT)
BEGIN
 DECLARE done INTEGER DEFAULT 0;
 DECLARE sscore INTEGER DEFAULT 0;
 DECLARE smaxscore INTEGER DEFAULT 0;
 DECLARE cur1 CURSOR FOR SELECT SUM(`score`), SUM(`maxscore`) FROM answertable WHERE `idParticipation`=partid;
 DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;

 OPEN cur1;
 REPEAT
  FETCH cur1 INTO sscore, smaxscore;
  UNTIL done = 1
 END REPEAT;
 CLOSE cur1;

 UPDATE participationtable SET `score`=sscore, `maxscore`=smaxscore WHERE `idParticipation`=partid;
END $$
DELIMITER ;

For completeness

the table name cannot be passed to a MySql cursor, at least not yet

http://forge.mysql.com/worklog/task.php?id=3433

the answer from below (corrected a bit)

DELIMITER $$

CREATE PROCEDURE updateTotalScores(IN participation_table VARCHAR(45), IN answer_table VARCHAR(45), IN part_id INT)
BEGIN
    SET @stmt_text=CONCAT("SELECT @score := SUM(`score`), @maxscore := SUM(`maxscore`) FROM ",
                         answer_table, " WHERE `idParticipation`=",  part_id);
    PREPARE stmt FROM @stmt_text;
    EXECUTE stmt;
    DEALLOCATE PREPARE stmt;

    SET @stmt_text=CONCAT("UPDATE ", participation_table, 
                        " SET `score`=?, `maxscore`=? WHERE `idParticipation`=", part_id);
    PREPARE stmt FROM @stmt_text;
    EXECUTE stmt USING @score, @maxscore;
    DEALLOCATE PREPARE stmt;
END $$

回答1:

I believe you cannot do it in this manner.

In order to achieve this, you should use Dynamic SQL.

Note that you cannot open a cursor using Dynamic SQL either. But in your case, there seems to be no need for a cursor.

If i understand your code correctly, you can just use user variables and probably achieve what you are trying to do using 2 Dynamically prepared statements.

  SET @stmt_text=CONCAT("SELECT @score = SUM(`score`), @maxscore=SUM(`maxscore`) FROM ",                
                         answertable, "WHERE `idParticipation`= ",  partid);
  PREPARE stmt FROM @stmt_text;
  EXECUTE stmt USING @a;

And then you update the values using the below statement

  SET @stmt_text=CONCAT("UPDATE", participationtable, " SET `score`=@score,  
                      `maxscore`=@maxscore WHERE `idParticipation`=", partid);

  PREPARE stmt FROM @stmt_text;
  EXECUTE stmt USING @a;

  DEALLOCATE PREPARE stmt;

Note: Please check the syntax. I cannot test it to verify it exactly but i hope you get the idea.

来源：https://stackoverflow.com/questions/3931287/mysql-pass-table-name-to-cursor-select

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mysql

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stored-procedures

mysql-error-1146