This blog post is an excerpt from premium MySQL Beginner content I am creating to help anyone learn how to use MySQL. Thank you for reading and please do provide feedback.
✔️ You may also be interested in the blog post, MySQL Beginners Series — The SELECT statement, which is a primer for this article.
Limit Rows with the WHERE clause
So far, we have been executing SELECT * and SELECT column_list types of queries. Not only are we retrieving all of the columns, but, also every row in the FROM clause table is returned. Oftentimes, it is not ideal to retrieve all of a tables’ rows since we may need a more specific set of them.
To filter the returned number of rows from a SELECT query, we use the WHERE clause with one or more search filter conditional tests, constraining the number of rows returned by the FROM clause table.
Comparison Operators
These conditional tests are applied to every row in the FROM clause table against column string, number, or date value data using any one or more of these basic comparisons operators:
- = : Equals to
- <> or != : Not equals to
- < : Less than
- > : Greater than
- <= : Less than or equals to
- >= : Greater than or equals to
(Additional conditional tests are possible using more advanced filtering mechanisms such as: LIKE, IN(), and BETWEEN. However, their discussion is beyond the scope of this introductory article.)
Each conditional test returns one of the following values:
- TRUE
- FALSE
- Unknown
For a row to be included in the result set, its specific conditional test (for however many columns are targeted) must evaluate to TRUE.
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Josh Otwell has a passion to grow as a PHP Developer, SQL expert, and technical blogger/writer.
Disclaimer: The majority of examples in this post, are performed in a personal development/learning workstation environment and should not be considered production quality or ready. Your particular goals and needs may vary. Like always, just because you can do something doesn’t mean you should. My opinions are my own.
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Learned, that the result of a SQL query may also be “unknown”, in addition to the familiar boolean values true and false.
Absolutely sir. Great point. Thank you for your valuable comment.