将变量传递到 CURSOR 的 SELECT 查询 (MySQL)

Question

我正在尝试下面的存储过程。但是，当我在“DECLARE cur1”行中传递实际列名时，SP 返回正确的值，但是当我传递变量名，即输入参数 (colName) 时，它返回 0。我在下面的代码中添加了 cmets。代码正确吗？

DROP PROCEDURE IF EXISTS test1.checkHardcodedField;
CREATE PROCEDURE test1.checkHardcodedField(IN textValue CHAR(10), colName CHAR(10), OUT counter VARCHAR(100))
BEGIN
  DECLARE done INT DEFAULT FALSE;
  DECLARE temp CHAR(16);
  DECLARE i INT DEFAULT 0;

  -- Issue with this statement, returns incorrect value.
  DECLARE cur1 CURSOR FOR SELECT colName FROM data1;   

  -- This statement works. MSH3 is actual column name
  -- DECLARE cur1 CURSOR FOR SELECT MSH3 FROM data1; 

  DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

  OPEN cur1;

  read_loop: LOOP
    FETCH cur1 INTO temp;

    IF done THEN
      LEAVE read_loop;
    END IF;
    IF temp = textValue THEN
      SET i = i + 1;
    END IF;
  END LOOP;

  SET counter = i;

  CLOSE cur1;
END;

Answer 1

CREATE PROCEDURE procedure_name (..., fieldname VARCHAR, ...)
BEGIN
    CREATE TEMPORARY TABLE tmp (field VARCHAR(10));
    SET @sql := CONCAT('INSERT INTO tmp SELECT ', fieldname, ' FROM tablename;');
    PREPARE stmt FROM @sql;
    EXECUTE stmt;
    DROP PREPARE stmt;
    BEGIN
        DECLARE cur CURSOR FOR SELECT field FROM tmp;
        ...
    END;
    DROP TABLE tmp;
END