What does having in sql mean?

The HAVING clause in SQL is used to filter aggregate results in aggregate queries. It is applied after the data has been grouped and the aggregate value has been calculated, filtering the rows based on the aggregation results, unlike the WHERE clause which is used to filter the original data before aggregation. The HAVING clause can be used to flexibly filter data based on the results of aggregate functions, but it can only be used in aggregate queries, and the columns of the aggregate function must be used in the GROUP BY clause.

HAVING clause in SQL

HAVING clause is used to aggregate results in SQL aggregation queries filter. It is similar to the WHERE clause, but the HAVING clause is applied after the data has been grouped and the aggregate value has been calculated.

Syntax:

<code class="sql">SELECT 聚合函数(列名)
FROM 表名
GROUP BY 分组列
HAVING 聚合条件;</code>

Usage:

The HAVING clause is used to filter the grouped results after calculating the aggregate value. It can filter out rows that meet specific conditions based on the aggregation results.

The difference with the WHERE clause:

The WHERE clause is used to filter the original data before aggregation, while the HAVING clause is used to filter the aggregation results after aggregation.

Example:

To find orders with sales greater than $1000, you can use the following query:

<code class="sql">SELECT SUM(amount) AS total_sales
FROM orders
GROUP BY customer_id
HAVING total_sales > 1000;</code>

Advantages:

• Allows filtering of data based on aggregated results.
• Provides greater flexibility and can filter data based on the results of aggregate functions.

Note:

• The HAVING clause can only be used in aggregate queries.
• The columns of the aggregate function must be used in the GROUP BY clause in order to group the results.

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