1. WHERE 条款：
WHERE 子句用于过滤表中的记录或在连接多个表时使用。只有那些满足 WHERE 子句中指定条件的记录才会被提取。它可以与 SELECT、UPDATE、DELETE 语句一起使用。
让我们考虑下表“学生”
Roll_no S_Name Age
1 a 17
2 b 20
3 c 21
4 d 18
5 e 20
6 f 17
7 g 21
8 h 17 考虑查询：
SELECT S_Name, Age FROM Student
WHERE Age >=18上述查询的输出是：
S_Name Age
b 20
c 21
d 18
e 20
g 21 2. 有条款：
HAVING 子句用于根据 HAVING 子句中的给定条件从组中过滤记录。满足给定条件的组将出现在最终结果中。 HAVING 子句只能使用
用 SELECT 语句。
让我们考虑上面提到的 Student 表并在其上应用带有子句：
SELECT Age, COUNT(Roll_No) AS No_of_Students
FROM Student GROUP BY Age
HAVING COUNT(Roll_No) > 1 上述查询的输出是：
Age No_of_Students
17 3
20 2
21 1 SQL 中 Where 和 Have 子句的区别：
| SR.NO. | WHERE Clause | HAVING Clause |
|---|---|---|
| 1. | WHERE Clause is used to filter the records from the table based on the specified condition. | HAVING Clause is used to filter record from the groups based on the specified condition. |
| 2. | WHERE Clause can be used without GROUP BY Clause | HAVING Clause cannot be used without GROUP BY Clause |
| 3. | WHERE Clause implements in row operations | HAVING Clause implements in column operation |
| 4. | WHERE Clause cannot contain aggregate function | HAVING Clause can contain aggregate function |
| 5. | WHERE Clause can be used with SELECT, UPDATE, DELETE statement. | HAVING Clause can only be used with SELECT statement. |
| 6. | WHERE Clause is used before GROUP BY Clause | HAVING Clause is used after GROUP BY Clause |
| 7. | WHERE Clause is used with single row function like UPPER, LOWER etc. | HAVING Clause is used with multiple row function like SUM, COUNT etc. |