Learning MySQL By Example

1. How to Retrieve Data From a Single Table

1.1. The Five Clauses of the SELECT Statement

1.2. Column Specifications

1.3. LIKE and REGEXP Operators

1.4. Arithmetic Operators

1.5. Column Aliases

1.6. Comparison Operators

1.7. IS NULL, BETWEEN, IN Operators

1.8. AND, OR, NOT Logical Operators

1.9. DISTINCT Clause

2. How to Retrieve Data from Multiple Tables

2.1. The JOIN Clause

2.2. Joining More Than Two Tables

2.3. The OUTER JOIN Clause

2.4. How to Code a UNION

3. Using Functions

3.1. Date Functions

3.2. Numeric Functions

3.3. String Functions

4. How to Insert, Update, Delete Data in Tables

4.1. The INSERT Clause With a Column List

4.2. The INSERT Clause Without a Column List

4.4. The UPDATE Clause With a Column List

4.4. The DELETE Clause

5. Summary Queries and Aggregate Functions

5.1. Aggregate Functions

5.2. Grouping Data

5.3. Simple GROUP BY Query

5.4. Improving the GROUP BY Query

5.5. Using the HAVING and WHERE Clauses Together

5.6. COUNT(column_name) and COUNT(*)

5.7. Using the DISTINCT Statement

6. Working With Subqueries

6.1. The Subquery In a SELECT Statement

6.2. The Subquery in an UPDATE statement

6.3. Create a Duplicate Table From An Existing Table

6.4. The Subquery In a Delete Statement

7.1. SQL View Explained

7.2. Benefits of Using Views

7.3. Views That Allow UPDATE Statements

8.1. SQL Indexes Explained

8.2. Clustered vs. Non-clustered Indexes

8.3. Create an Index in Workbench Using an ERD

8.4. How to Manually Add an Index to an Existing Table

5.5

Using the HAVING Clause

Filtering Aggregate Functions With The HAVING Clause

The HAVING CLAUSE allows you to use an aggregate function as a filter. This is not allowed in a WHERE clause.
Any columns or expressions you want to use in a HAVING clause, MUST BE DEFINED IN THE SELECT CLAUSE as well.

Code Sample:

USE bike; SELECT category_id, AVG(list_price) FROM product GROUP BY category_id HAVING AVG(list_price) > 1000

Output:

We previously discussed the preceding lines of code for this query so we will focus solely on the HAVING clause.

HAVING AVG(list_price) > 1000

The HAVING clause executes after the GROUP BY clause but before the SELECT
If you use an aggregate function in the HAVING clause, you must include the same aggregate function in the SELECT
If you reference a column or expression in the HAVING clause, you must include the same column or expression in the SELECT
You cannot use aggregate functions in a WHERE clause

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