sql 合并查询结果

在使用js报表工具的时候,常常需要提供json数据进行显示,

在sql查询的时候就需要构造合适的查询结果出来;

就用到了合并两个没有关联关系的表数据,

SELECT
    SUM(a1.amount) AS amount,
    a1.date
    FROM
    ((SELECT
    SUM(amount) AS amount,
    DATE_FORMAT(time,'%Y-%m-%d') AS date
    FROM a 
    GROUP BY date)
    UNION ALL
    (SELECT -SUM(b.VALUE) AS s2,
    DATE_FORMAT(b.time,'%Y-%m-%d') AS d2
    FROM
    b
    GROUP BY d2)) AS a1
    GROUP BY a1.date
//a表收款,b表付款,计算每天的收益(收款-付款)
//根据日期(天)分组,对两个表中的金额进行计算
//注意时间字段名称,a表相同位置的字段会覆盖b表字段名称,所以使用union要求两个表有相同的字段
//最后根据合并后时间进行分组,计算收益(计算差)

使用union 或union all
如select * from a union all select * from b 竖排合并两个表的数据
显示格式如:
a     date

-204   2015-07-06
220    2015-07-15
-60    2015-07-16
220    2015-07-17

//另外一种情况,根据不同条件得到的值赋予不一样的别名(在不同的列显示)

SELECT
    a.date,
    sum(a.c1) AS s1,
    SUM(a.c2) AS s2
    FROM(
    SELECT
    DATE_FORMAT(b.time, '%Y-%m-%d') AS date,
    IFNULL((
    CASE b.sta
    WHEN 0 THEN COUNT(*) END),0
    ) AS c1,
    IFNULL((
    CASE b.sta
    WHEN 1 THEN COUNT(*) END),0
    ) AS c2
    FROM  b
    GROUP BY b.sta,date
    ) AS a
    GROUP BY a.date
//根据类型sta=0/=1,时间分组,统计个数

得到的数据格式:

date               s1 s2

2015-07-06    4   1
2015-07-08    0   1
2015-07-15    0   1
2015-07-16    1   3