What is the function of the having clause in the database

This article mainly introduces the role of the having clause in the database, the article is very detailed, has a certain reference value, interested friends must read it!

The function of the where clause is to remove the rows that do not meet the where condition before grouping the query results, that is, to filter the data before grouping, the condition cannot contain a cluster function, and the where condition is used to display specific rows.

The role of the having clause is to filter groups that meet the criteria, that is, to filter data after grouping, which often contains clustering functions, to display specific groups using having conditions, or to group using multiple grouping criteria.

The having clause qualifier is already on the columns and aggregate expressions defined in the SELECT statement. Typically, you need to reference the aggregate value by repeating the aggregate function expression in the having clause, as you did in the SELECT statement.

For example:

SELECT A COUNT (B) FROM TABLE GROUP BY A HAVING COUNT (B) > 2 is all the contents of the article "what is the function of having clauses in the database?" Thank you for reading! Hope to share the content to help you, more related knowledge, welcome to follow the industry information channel!