The WHERE Clause in MySQL
The WHERE Clause is used to filter only those records that are fulfilled by a specific condition given by the user, in other words, the SQL WHERE Clause is used to restrict the number of rows affected by a SELECT, UPDATE or DELETE query.
I find that the WHERE Clause is very useful and helps in improving a query’s run time. By filtering the data to only include the observations you need or a subset of the information you require for testing; it dramatically improves your query speed.
The basic syntax of the WHERE Clause is
SELECT Column1, Column2, ….
FROM Table_Name
WHERE Condition
Example
Let us consider the following table “Students” with five columns ‘FirstName’, ‘LastName’, ‘Age’, ‘Class’ and ‘Year’.
To select all the rows where the “Year” is “1”, we will use the following code:
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SELECT FirstName, LastName, Age, Class, Year
FROM Students
WHERE Year = 1;
This syntax will give the following result below:
Furthermore, a subquery can be written in a WHERE Clause to qualify a column against a set of rows.
An example of a syntax using subqueries in the WHERE Clause can be seen below. It uses the European soccer database called “Match”.
For further information on the WHERE Clause please watch the video below.
