我是SQl新手，尝试自己学习。

我正在学习SQL中if和else语句的用法

这里是我正在尝试使用的数据，如果在下表中，或者声明，我希望根据年龄使用sql查询更新评论，假设年龄在22到25之间，评论“下毕业”

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

---

如何使用案例

试用CASE声明

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

---

我可能会去CASE声明

就像是

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

---

按照您的要求，我们不能使用if ... else语句。 Case..when声明将是最合适的一个。 另一件事我们无法在任何查询中使用if ... else（我的意思是在选择，插入，更新内）。

和你的

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

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