mysql - 无法在 Concat select Prepared 语句中传递参数值

Question

我发现存储过程不只执行这部分:

          SET @sql 
          = CONCAT('SELECT TraineeID, ', @sql, ' 
                    from tbl_submit_coursefee c
                    where c.BatchID='BID'
                    group by c.TraineeID');

在 where 子句 '' 中，引号不允许并且没有引号查询返回空，但是如果我将参数值直接放在 where 子句中，那么它就可以工作。我真的很喜欢这个。

这是我准备好的声明(工作正常):

SET @sql = NULL;    
SELECT
     GROUP_CONCAT(DISTINCT
     CONCAT ('MAX(IF(BillNo = ''', BillNo, ''', CRA, NULL)) AS `Inv.', BillNo, '`') 
         )  INTO @sql
    FROM tbl_submit_coursefee
    WHERE BatchID="ID-Welding/FMMTTC-01M/R8/01";

    SET @sql 
      = CONCAT('SELECT TraineeID, ', @sql, ' 
                from tbl_submit_coursefee c
                where c.BatchID="ID-Welding/FMMTTC-01M/R8/01"
                group by c.TraineeID');

    PREPARE stmt FROM @sql;
    EXECUTE stmt;
    DEALLOCATE PREPARE stmt;

将此语句放入存储过程时(不工作):

DELIMITER @@
DROP PROCEDURE GetRetainment @@
CREATE PROCEDURE vtproject.GetRetainment
(IN `BID` VARCHAR(100))
BEGIN
    SET @sql = NULL;
    SELECT
        GROUP_CONCAT(DISTINCT
            CONCAT ('MAX(IF(BillNo = '', BillNo, '', CRA, NULL)) AS `Inv.', BillNo, '`') 
        )   INTO @sql
    FROM tbl_submit_coursefee
    WHERE BatchID=BID;

    SET @sql 
      = CONCAT('SELECT TraineeID, ', @sql, ' 
                from tbl_submit_coursefee c
                where c.BatchID='BID'
                group by c.TraineeID');

    PREPARE stmt FROM @sql;
    EXECUTE stmt;
    DEALLOCATE PREPARE stmt;
END @@ 
DELIMITER ; 

如果我在 prepare stmt FROM @sql 之前 select @sql 然后输出如下:

SELECT TraineeID, MAX(IF(BillNo = 1, CRA, NULL)) AS `Inv.1`,MAX(IF(BillNo = 2, CRA, NULL)) AS `Inv.2`,MAX(IF(BillNo = 3, CRA, NULL)) AS `Inv.3`,MAX(IF(BillNo = 4, CRA, NULL)) AS `Inv.4`,MAX(IF(BillNo = 5, CRA, NULL)) AS `Inv.5`,MAX(IF(BillNo = 6, CRA, NULL)) AS `Inv.6`,MAX(IF(BillNo = 7, CRA, NULL)) AS `Inv.7` from tbl_submit_coursefee c where c.BatchID=BID group by c.TraineeID

Answer 1

你需要转义引号，像这样:

SET @sql 
= CONCAT('SELECT TraineeID, ', @sql, ' 
from tbl_submit_coursefee c 
where c.BatchID=''',BID,''' 
group by c.TraineeID');

根据文档:http://dev.mysql.com/doc/refman/5.7/en/string-literals.html