The SQL Server
HAVING operator is used in conjunction with the GROUP BY clause to filter the results of an aggregation function based on a condition.
HAVING operator is similar to the
WHERE clause, but it is used specifically for filtering aggregated data.
In SQL Server, aggregation functions such as COUNT, SUM, AVG, MIN, and MAX are used to perform calculations on groups of rows. The
GROUP BY clause is used to group the data based on one or more columns, and the result of the aggregation function is calculated for each group.
HAVING operator is then used to filter the results based on a condition that is applied to the aggregated data. This condition can be any valid expression that evaluates to a Boolean value, such as an arithmetic expression, a comparison, or a logical operator.
The syntax for the
HAVING operator is as follows:
SELECT column_name(s), aggregation_function(column_name)
GROUP BY column_name(s)
For example, suppose we have a table named "Sales" that contains data about the sales of various products in different regions. We want to find the total sales for each region, but we only want to include regions where the total sales are greater than $10,000. We can use the following SQL statement:
SELECT Region, SUM(SalesAmount) AS TotalSales
GROUP BY Region
HAVING SUM(SalesAmount) > 10000;
This statement will group the sales data by region and calculate the total sales for each region. The
HAVING operator will then filter the results to only include regions where the total sales are greater than $10,000.
It is important to note that the
HAVING operator is only used with the
GROUP BY clause and cannot be used without it. Additionally, the HAVING operator is applied after the GROUP BY clause, so it can only be used to filter aggregated data.
SELECT c.customer_id, c.amount
FROM contracts c
WHERE c.amount < 2500
GROUP BY c.customer_id, c.amount
HAVING MIN(c.amount) > 1000 ;
In summary, the SQL Server
HAVING operator is a powerful tool for filtering aggregated data based on a condition.