select id,name,(case sex when '1' then '男' when '2' then '女' else '其他' end) from student; 这两种方法可以实现相同的功能. 简单Case函数的写法比较简单,但是和case搜索函数相比,功能方面会有些限制,比如判断式. 还有一个需要注意的问题,Case函数只返回第一个符合条件的值,剩下的Case部分将会被...
CASE可能是 SQL 中被误用最多的关键字之一。虽然你可能以前用过这个关键字来创建字段,但是它还具有更多用法。例如,你可以在WHERE子句中使用CASE。 首先让我们看一下CASE的语法。在一般的SELECT中,其语法如下: SELECT<myColumnSpec>= CASE WHEN<A>THEN<somethingA> WHEN<B>THEN<somethingB> ELSE<somethingE> END...
SELECT country, SUM( CASE WHEN sex = '1' THEN population ELSE 0 END), --男性人口 SUM( CASE WHEN sex = '2' THEN population ELSE 0 END) --女性人口FROMTable_A GROUP BY country; 这样我们使用Select,完成对二维表的输出形式,充分显示了Case函数的强大。
insert into test_case2 values(1,'aa');insert into test_case2 values(2,'bb');insert into test_case2 values(3,'cc');insert into test_case2 values(6,'ee');commit;4、两表关联，并编写case when的语句 select t.*,case when b.id is not null then '存在' else '不存在' e...
SELECTcolumn1, column2, ...CASEWHENcondition1THENresult1WHENcondition2THENresult2-- Add more WHEN conditions and results as neededENDASalias_nameFROMtable_name; We can add as manyWHEN ... THENconditions as required in theCASEstatement. For example, ...
The case statement in SQL returns a value on a specified condition. We can use a Case statement in select queries along with Where, Order By, and Group By clause. It can be used in the Insert statement as well. In this article, we would explore the CASE statement and its various use...
Let’s illustrate with an example. The following SQL statement will return “Monday” if today is a Monday, otherwise it returns “Not a Monday”. SETDATEFIRST1-- first day of the week is a MondaySELECTCASEWHENDATEPART(WEEKDAY,GETDATE())=1THEN'Monday'ELSE'Not a Monday'END ...
SQL SELECT Statement - Learn the SQL SELECT statement to retrieve data from your database efficiently. Explore examples and syntax to master SQL queries.
GOSELECT ProductNumber, Category =CASE ProductLineWHEN 'R' THEN 'Road'WHEN 'M' THEN 'Mountain'WHEN 'T' THEN 'Touring'WHEN 'S' THEN 'Other sale items'ELSE 'Not for sale'END,NameFROM Production.ProductORDER BY ProductNumber;GO这句话其实意思很简单，就是对每一行中的ProductLine...
Use CASE WHEN statement in SELECT /* mysql> SELECT Name, RatingID AS Rating, -> CASE RatingID -> WHEN 'R' THEN 'Under 17 requires an adult.' -> WHEN 'X' THEN 'No one 17 and under.' -> WHEN 'NR' THEN 'Use discretion when renting.' -> ELSE 'OK to rent to minors.' -> ...