SQL 中 Where 子句和 Having 子句的区别
原文:https://www . geesforgeks . org/where-and-having-in-SQL 子句的区别/
1。WHERE 子句: WHERE 子句用于从表中筛选记录，或者在连接多个表时使用。只有满足 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
上述查询的输出为:
S_Name Age
b 20
c 21
d 18
e 20
g 21
2。HAVING 子句: HAVING 子句用于根据 HAVING 子句中的给定条件从组中筛选记录。那些满足给定条件的组将出现在最终结果中。HAVING 子句只能与 SELECT 语句一起使用 。
让我们考虑上面提到的学生表，并在上面应用有子句:
SELECT Age, COUNT(Roll_No) AS No_of_Students
FROM Student GROUP BY Age
HAVING COUNT(Roll_No) > 1
上述查询的输出为:
Age No_of_Students
17 3
20 2
21 1
SQL 中 Where 子句和 Having 子句的区别:
| SR number | WHERE clause | 拥有子句 | | --- | --- | --- | | 1。 | WHERE clause is used to filter records from the table according to specified conditions. | The HAVING clause is used to filter records from a group according to specified criteria. | | 2。 | The WHERE clause can be used without the GROUP BY clause | HAVING clause cannot be used without GROUP BY clause. | | 3。 | WHERE clause is implemented in row operation | HAVING clause implemented in column operation | | 4。 | WHERE clause cannot contain aggregate function | HAVING clause can contain aggregate function. | | 5。 | The WHERE clause can be used with SELECT, UPDATE and DELETE statements. | HAVING clause can only be used with SELECT statement. | | 6。 | The WHERE clause is used before the GROUP BY clause | HAVING clause is used after GROUP BY clause. | | 7。 | The WHERE clause is used with single-line functions such as UPPER and LOWER. | HAVING clause is used with multi-line functions such as SUM and COUNT. |版权属于：月萌API www.moonapi.com，转载请注明出处
