MySQL Where Clause

 Introduction

MySQL is an open-source relational database management system (RDBMS) that is widely used for various applications, ranging from small-scale websites to large-scale enterprise systems. MySQL provides various options to retrieve data from tables, such as using SELECT queries with WHERE clauses. In this article, we will discuss the SELECT query with WHERE clauses in MySQL and how to use them effectively.

What is SELECT Statement in MySQL

The SELECT statement is a fundamental SQL statement used to retrieve data from one or more tables in a database. The SELECT statement retrieves data from a table and returns it to the user or application. The basic syntax of the SELECT statement is as follows:

In this syntax, column1, column2, etc. are the names of the columns in the table that we want to retrieve data from. The table_name is the name of the table from which we want to retrieve data. We can also use the * wildcard character to retrieve all columns from a table.

For example, the following query retrieves all columns from the "users" table:

The SELECT query can also be used to retrieve data from multiple tables using a JOIN clause. We will cover this in more detail in a later section.

What is the WHERE clause in MySQL

The WHERE clause is used in the SELECT statement to filter rows based on a specified condition. The WHERE clause can be used to filter rows based on one or more conditions. If the WHERE clause is not specified, all rows in the table will be returned. The basic syntax of the SELECT statement with a WHERE clause is as follows:

The condition specified in the WHERE clause is evaluated for each row in the table. Only the rows that satisfy the condition are returned in the result set. The condition can be any expression that evaluates to a Boolean value (TRUE or FALSE).

In Easy Language:

• The Where clause is used to filter records.
• It is used to extract only those records that fulfill a specified condition.

Using the SELECT statement with WHERE clause in MySQL

To use the SELECT statement with a WHERE clause, we need to specify the column(s) we want to retrieve data from and the condition(s) that should be satisfied for the rows to be included in the result set. Let's consider an example where we have a table named "customers" with the following columns:

• id(integer)
• name(varchar)
• email(varchar)
• age(integer)

Suppose we want to retrieve the name and email of all customers who are above the age of 25. We can use the following SQL statement:

In this statement, we have specified the columns "name" and "email" that we want to retrieve data from. We have also specified the condition "age > 25" in the WHERE clause, which means that only the rows where the age column is greater than 25 will be returned.

Comparison Operators in WHERE Clause:

The WHERE clause supports several comparison operators that can be used to specify the condition. The following table lists the comparison operators that are supported by MySQL:

Let's take a look at some examples of using comparison operators in the WHERE clause in this link.