SQL，多个if语句，还是其他语句？

Question

我是SQl的新手，我试着自己学习。

我正在学习if和the语句在SQL中的用法。

下面是我试图使用的数据，在下表中的if或let语句中，我希望使用sql查询根据年龄更新注释，如果年龄在22岁到25岁之间，则注释“未毕业”。

Age: 26 to 27, comments " post graduate"
Age: 28 to 30, comments "working and single"
Age: 31 to 33, comments " middle level manager and married"

表名:人员

personid  lastname  firstname   age comments
1         Cardinal  Tom         22
2         prabhu    priya       33
3         bhandari  abhijeet    24
4         Harry     Bob         25
5         krishna   anand       29
6         hari      hara        31
7         ram       hara        27
8         kulkarni  manoj       35
9         joshi     santosh     28

Answer 1

如何用例

用CASE语句尝试

Select personid,lastname,firstname,age,
       Case when age between 26 and 27 then 'post graduate'
            when age between 28 and 30 then 'working and single' 
            when age between 31 and 33 then ' middle level manager and married' 
            Else 'Nil'
       End comments 
from persons

Answer 2

我可能会用一个案例语句

有点像

SELECT  *,
        CASE
            WHEN age BETWEEN 22 AND 25 
                THEN 'under graduate'
            WHEN age BETWEEN 26 AND 27
                THEN 'post graduate'
            WHEN age BETWEEN 28 AND 30 
                THEN 'working and single'
            WHEN age BETWEEN 31 AND 33
                THEN 'middle level manager and married'
            ELSE 'TADA'
        END Comment
FROM    persons

Answer 3

根据您的要求，我们不能使用if...else语句。Case..when语句将是最合适的。还有一件事我们不能在任何查询中使用if...else (我指的是在select、insert、update内部)。

还有你的

Select personid,lastname,firstname,age,
   Case when age between 26 and 27 then 'post graduate'
   Case when age between 28 and 30 then 'working and single' 
   Case when age between 31 and 33 then ' middle level manager and married' 
   Else 'Nil'
   End comments 
from persons