SQL having clause

Source: Internet
Author: User
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    • SQL having syntax
References

Http://www.w3school.com.cn/ SQL/SQL _having.asp

Having clause

The reason for adding the having clause in SQL is,The where keyword cannot be used with the aggregate function..

SQL having syntax
 
SelectColumn_name, aggregate_function (column_name)FromTable_nameWhereColumn_name operator ValueGroup ByColumn_nameHavingAggregate_function (column_name) operator Value
SQL having instance

We have the following "orders" table:

O_id Orderdate Orderprice Customer
1 2008/12/29 1000 Bush
2 2008/11/23 1600 Carter
3 2008/10/05 700 Bush
4 2008/09/28 300 Bush
5 2008/08/06 2000 Adams
6 2008/07/21 100 Carter

Now, we want to find customers whose total order amount is less than 2000.

We use the following SQL statement:

SelectCustomer,Sum(Orderprice)FromOrdersGroup ByCustomerHaving Sum(Orderprice)<2000

The result set is similar:

Customer Sum (orderprice)
Carter 1700

Now we want to find the customer "Bush" or "Adams" with more than 1500 of the total order amount.

We add a common where clause to the SQL statement:

SelectCustomer,Sum(Orderprice)FromOrdersWhereCustomer='Bush' OrCustomer='Adams'Group ByCustomerHaving Sum(Orderprice)>1500

Result set:

Customer Sum (orderprice)
Bush 2000
Adams 2000
Usage of where and having statements
    1. Before a group by statement, SQL calculates the where statement before grouping.  
    2. Having statement after the group by statement, SQL calculates the having statement after the group.

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