Question

我正在尝试创建一个从表中返回值的函数

CREATE DEFINER =  `root`@`localhost` FUNCTION  `GETINFO` (
    `INFO_ID` BIGINT( 20 ) ,
    `ENTITY` VARCHAR( 255 ) ,
    `ANCHOR` VARCHAR( 255 )
) RETURNS DOUBLE DETERMINISTIC READS SQL DATA SQL SECURITY DEFINER BEGIN DECLARE var_name DOUBLE;

    # default value
    SET var_name = -999.999;

    # get desired value in database
    SELECT MAX(`value`) 
        INTO var_name
        FROM  `mydata` 
        WHERE `info`   = INFO_ID
          AND `entity` = ENTITY
          AND `anchor` = ANCHOR 
        LIMIT 0 , 1;

    RETURN var_name;

    END

当我尝试调用该函数时：

case 1) SELECT GETINFO(2, "134604843861826", "uniq") <========= real parameters, works fine
case 2) SELECT GETINFO(2, "1346048438618",   "uniq") <========= just removed some chars to force error, but returns same value as case 1
case 3) SELECT GETINFO(12312, "123",         "1233") <========= all params incorrect, now it returns NULL as expected

在案例2中

问题，为什么它不尊重WHERE子句并返回NULL？

Answer 1

问题是这些问题：

     AND `entity` = ENTITY
      AND `anchor` = ANCHOR

这些在过滤方面做 nothing ，因为它们都引用了表中的列。您应该始终在函数中为参数添加前缀以避免此问题。

CREATE DEFINER =  `root`@`localhost` FUNCTION  `GETINFO` (
    `param_INFO_ID` BIGINT( 20 ) ,
    `param_ENTITY` VARCHAR( 255 ) ,
    `param_ANCHOR` VARCHAR( 255 )
) RETURNS DOUBLE DETERMINISTIC READS SQL DATA SQL SECURITY DEFINER BEGIN DECLARE var_name DOUBLE;

    # default value
    SET var_name = -999.999;

    # get desired value in database
    SELECT MAX(`value`) 
        INTO var_name
        FROM  `mydata` 
        WHERE `info`   = param_INFO_ID
          AND `entity` = param_ENTITY
          AND `anchor` = param_ANCHOR 
        LIMIT 0 , 1;

    RETURN var_name;

    END

自定义函数不尊重WHERE子句

1 个答案: