MySQL的类似if else 的判断

CASE WHEN 

...条件

THEN 

...结果

ELSE

LEFT( monthDate,4) 左截取4个字符或RIGHT(monthDate,4)右截取4个字符，可以用这个对日期进行分组。

DATE_FORMAT(NOW(),'%Y')日期的格式化，如果需要对日期分组时，不要用这个，会出问题的。

SELECT monDate,f1, n1 FROM (SELECT DATE_FORMAT(d1,'%Y-%m') AS monDate ,SUM(f1) as f1 ,SUM(n1) as n1 FROM (SELECT t.date AS d1, (SUM(CASE WHEN t.num = 2 THEN t.FLOW_IN
ELSE (t.FLOW_IN)*2 END) + SUM(CASE WHEN t.num = 2 THEN t.FLOW_OUT ELSE (t.FLOW_OUT)*2 END)) AS f1 FROM (SELECT COUNT(pk) AS num, DATE(DATE) AS DATE ,
SUM(FLOW_IN)/2 AS FLOW_IN , SUM(FLOW_OUT)/2 AS FLOW_OUT FROM moa_control_flow WHERE 1=1 GROUP BY DATE(DATE) ORDER BY
DATE ASC ) AS t WHERE 1 = 1 GROUP BY t.date) AS f, (SELECT t.date AS d2, SUM(CASE WHEN t.num = 2 THEN t.num_sum
ELSE (t.num_sum)*2 END) AS n1, SUM(CASE WHEN t.num = 2 THEN t.num_in ELSE (t.num_in)*2 END) AS n2, SUM(CASE
WHEN t.num = 2 THEN t.num_out ELSE (t.num_out)*2 END) AS n3 FROM (SELECT COUNT(pk) AS num, DATE(DATE) AS DATE ,
SUM(num_sum)/2 AS num_sum , SUM(num_in)/2 AS num_in, SUM(num_out)/2 AS num_out FROM moa_control_session_conn
WHERE 1=1 GROUP BY DATE(DATE) ORDER BY DATE ASC ) AS t WHERE 1 = 1 GROUP BY t.date ) AS c WHERE f.d1=c.d2 GROUP BY LEFT(d1,7)) AS t
where LEFT(t.monDate,4) = DATE_FORMAT(NOW(),'%Y')