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This article mainly introduces "what is the difference between where and having in sql sentences". In daily operation, I believe that many people have doubts about the difference between where and having in sql sentences. The editor consulted all kinds of materials and sorted out simple and easy-to-use methods of operation. I hope it will be helpful to answer the questions of "what is the difference between where and having in sql sentences?" Next, please follow the editor to study!

HAVING first groups and then filters records, and WHERE filters records before aggregation. that is, it acts before the GROUP BY clause and the HAVING clause, while the HAVING clause filters the group records after aggregation.

The object of action is different. The WHERE clause acts on tables and views, and the HAVING clause acts on groups. WHERE selects input rows before grouping and aggregation calculation (therefore, it controls which rows enter the aggregation calculation), while HAVING selects grouped rows after grouping and aggregation. Therefore, the WHERE clause cannot contain an aggregate function; there is no point in trying to use an aggregation function to determine which rows are input to the aggregation operation. In contrast, the HAVING clause always contains aggregate functions. (strictly speaking, you can write HAVING clauses that do not use aggregation, but this is in vain. The same conditions can be used more effectively in the WHERE phase. (for example:

Select * from tablename where id > 1; and

Select * from tablename having id > 1

There is no difference between the two query results. Having is not recommended

To sum up, there are two sentences:

The WHERE statement comes before the GROUPBY statement; SQL evaluates the WHERE statement before grouping.

The HAVING statement comes after the GROUPBY statement; SQL evaluates the HAVING statement after grouping.

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