case when .. then ... when ... then ... else end
case when:類似於if,根據條件返回值
case when sex = '0' then '女' when sex='1' then '男' end
或者
case when sex='0' then '女' else '男' end
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SUBSTRING_INDEX(字段,分隔符,取段位置)
字段名稱:var = '123_232_aaa_ewrwe,123'
SUBSTRING_INDEX(var,'_',1) = 123
SUBSTRING_INDEX(var,'_',2) = 123_232
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獲取系統當前時間,格式爲 yyyy-MM-dd HH:mm:ss
now()、current_timestamp() :語句開始執行的時間
sysdate():函數開始執行的時間
unix_timestamp(current_timestamp()) 將時間戳換成秒
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REPLACE('123.123.345','.','') 將字符'.'換成空字符
結果等於 123123345
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timediff:求得兩個時間的時間差,返回結果爲 yyyy-MM-dd HH:mm:ss
timediff(NOW(),'2019-07-10 10:32:03')
TIME_TO_SEC:將轉換爲秒
TIME_TO_SEC('00:01:19') = 79
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date_format:輸出時間格式
date_format(NOW(),'%Y-%m-%d %H:%i:%s') = 2019-07-10 10:38:12
date_format(NOW(),'%Y-%m-%d) = 2019-07-10