mysql中if（）函數使用

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      在mysql中if()函數的用法類似於java中的三目表達式，其用處也比較多，具體語法如下：

IF(expr1,expr2,expr3)，如果expr1的值為true，則返回expr2的值，如果expr1的值為false，

則返回expr3的值。

       其經常判斷查詢出來的值，示例；

mysql> select name,if(sex=0,'女','男') as sex from student;
+-------+-----+
| name  | sex |
+-------+-----+
| name1 | 女  |
| name2 | 女  |
| name3 | 男  |
| name4 | 女  |
+-------+-----+
4 rows in set (0.00 sec)

       其也經常用到判斷的關聯條件中，其示例如下：

SELECT  s.SCHOOL_CITY as schoolCity,
        s.SCHOOL_COUNTY as schoolCounty,
        count(DISTINCT `s`.`SCHOOL_ID`) as schoolNum,
        sum(m.duration) as sumDuration,
        sum(`m`.`VIEWERCOUNT`) as viewLiveSum,
        sum(m.replayViewerCount)as reViewSum,
        sum(m.praisecount) as sumpraise,
        sum(`m`.`VIEWERCOUNT`+m.replayViewerCount) as viewSum
         from ((tbl_hbb_mobile_live_statistics m join tbl_hbb_resource_visit_map v) join tbl_school_info s)
    where`m`.`RESOURCEID`= `v`.`RESOURCEID` 
        and if((`v`.`rangeTYPE`= '2'),(`v`.`rangeID`= `s`.`SCHOOL_ID`),(`v`.`parentId`= `s`.`SCHOOL_ID`))