sql的 case語句
在SQL的世界中CASE語句相當於if -----else 語句。
Case具有兩種格式。簡單Case函式和Case搜尋函式。
--簡單Case函式 CASE sex WHEN '1' THEN '男' WHEN '2' THEN '女' ELSE '其他' END --Case搜尋函式 CASE WHEN sex = '1' THEN '男' WHEN sex = '2' THEN '女' ELSE '其他' END
這兩種方式,可以實現相同的功能。
1、舉例:查詢發生時間是9月份的各時間段的數量
SELECT
COUNT(resum.id) AS number,
( CASE WHEN DATE_FORMAT(resum.happenedTime,'%H') >'8' AND DATE_FORMAT(resum.happenedTime,'%H') <= '16' THEN '8-16組'
WHEN DATE_FORMAT(resum.happenedTime,'%H') > '16' AND DATE_FORMAT(resum.happenedTime,'%H') <= '24' THEN '16-0組'
WHEN DATE_FORMAT(resum.happenedTime,'%H') > '0' AND DATE_FORMAT(resum.happenedTime,'%H') <= '8' THEN '0-8組'
END) AS projectBreakdown
FROM `naers_eventsresume` resum
INNER JOIN sys_hospital hos ON resum.hospitalId=hos.hospital_id AND hos.status=0
WHERE resum.STATUS=3 AND eventType=1
AND (resum.happenedTime BETWEEN '2018-09-01' AND CONCAT('2018-09-30',' 23:59:59'))
GROUP BY projectBreakdown;
結果如下:
2、查詢9月份的事件等級I,II,III,IV的數量
SELECT eventlevel,COUNT(id) FROM `naers_events_ddzc`
WHERE `status`='3'
AND `happenedTime`>='2018-09-01 00:00:00'
AND `happenedTime`<='2018-09-30 23:59:59'
AND `type`='1'
GROUP BY eventlevel;