mysql - 如何连接字符串并将字符串转换为日期？

Question

请查看我的存储过程代码.

CREATE DEFINER=`ninjaboy`@`%` PROCEDURE `getMonthlyTotalScore`(IN ninjaId int,  IN month int, IN year int)
BEGIN
    DECLARE startDate DATE;
    DECLARE endDate DATE;
    DECLARE maxDay INTEGER;

    SELECT DAY(LAST_DAY(year + '-' + month + '-01')) INTO maxDay;

    SET startDate = year + '-' + month + '-01';
    SET endDate = year + '-' + month + '-' + maxDay;

    SELECT SUM(SCORE) FROM NINJA_ACTIVITY WHERE NINJA_ID = ninjaId AND DATE BETWEEN startDate AND endDate ORDER BY DATE;
END

测试数据:

NINJA_ACTIVITY_ID | NINJA_ID | SCORE | DATE
1                   1          24      2012-05-01
2                   1          36      2012-05-06
3                   1          29      2012-05-11

功能调用: call getTotalMonthlyScore (1, 5, 2012)

我试图得到任何忍者的月度分数基于ninjaId.

为什么不工作？知道我哪里出错吗？

Answer 1

CONCAT()是关键.

之前:

mysql> CREATE  PROCEDURE `getMonthlyTotalScore`(IN ninjaId int,  IN month int, IN year int)
        -> BEGIN
        ->     DECLARE startDate DATE;
        ->     DECLARE endDate DATE;
        ->     DECLARE maxDay INTEGER;
        -> 
        ->     SELECT year + '-' + month + '-01'; #NOTE THIS
        -> 
        ->     
        -> END;    
        -> |
    Query OK, 0 rows affected (0.00 sec)

    mysql> call getMonthlyTotalScore(1,5,2012);
        -> |
    +----------------------------+
    | year + '-' + month + '-01' |
    +----------------------------+
    |                       2016 |
    +----------------------------+
    1 row in set (0.00 sec)

后:

mysql> CREATE  PROCEDURE `getMonthlyTotalScore`(IN ninjaId int,  IN month int, IN year int)
    -> BEGIN
    ->     DECLARE startDate DATE;
    ->     DECLARE endDate DATE;
    ->     DECLARE maxDay INTEGER;
    -> 
    ->     SELECT CONCAT(year,'-',month,'-01'); # NOTE THIS
    -> 
    ->     
    -> END;    |
Query OK, 0 rows affected (0.00 sec)

mysql> call getMonthlyTotalScore(1,5,2012);
    -> |
+------------------------------+
| CONCAT(year,'-',month,'-01') |
+------------------------------+
| 2012-5-01                    |
+------------------------------+
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)