sum(case when ct.tradeTotal >= 0 then 1 else 0 end)的意思

 

String hql = "select new com.ks.admin.report.dto.ReportMonthWithDrawalDto(" +
				"count(*)," + "sum(ct.tradeTotal)," + "sum(case when ct.tradeTotal >= 0 then 1 else 0 end)," + "sum(case when ct.tradeTotal >= 0 then ct.tradeTotal else 0 end)" + ") " + "from CustTrade ct " + "where ct.tradeType = 'DR' " + "and ct.tradeTime between ? and ? " + "and ct.tradeDesc like '%提現%'";

count（*）返回的是Long類型，Sum(Double類型)返回Double類型， sum(case when ct.tradeTotal >= ? then ct.1 else 0 end) 返回Long類型。

 

sum(case when ct.tradeTotal >= 0 then 1 else 0 end)的意思是當ct.tradeTotal>=0的時候會返回1，否則返回0，而sum會累加，因為0累加之后還是0，所以只會返回1的累加之后才會改變值，因此這表示統計ct.tradeTotal>=0的數據總數。為什么不用count呢？因為試驗過，count里面無法用條件。

sum(case when ct.tradeTotal >= 0 then ct.tradeTotal else 0 end)的意思是當ct.tradeTotal>=0的時候返回ct.tradeTotal的值，否則返回0，同理，如果條件成立，會累加ct.tradeTotal>=0的值。

 

如果以上描述有錯誤，請提出，一起共同學習。