WHERE Clause in SQL

WHERE Clause in SQL

The WHERE clause is an essential component of SQL queries used to filter data based on specified conditions. It allows you to select records from a table that meet specific criteria, resulting in a subset of data that satisfies the given conditions.

Syntax:

sql
SELECT column1, column2, ...
FROM table_name
WHERE condition;

Explanation:

The WHERE clause is placed after the SELECT statement and before the FROM clause. It consists of a condition that evaluates to either true or false for each row in the table. Rows that satisfy the condition are included in the result set.

Example:

Let's consider a hypothetical "employees" table with the following columns: "id", "name", "age", and "department".

sql
SELECT id, name, age
FROM employees
WHERE age > 30;

In the above example, the query retrieves the "id," "name," and "age" columns from the "employees" table, but only for the rows where the "age" is greater than 30. It filters out any rows that do not meet the specified condition.

You can also combine multiple conditions using logical operators such as AND and OR:

sql
SELECT id, name, age
FROM employees
WHERE age > 30 AND department = 'IT';

This query retrieves the records where the age is greater than 30 and the department is "IT."

Furthermore, you can use comparison operators like "=" (equal to), "<" (less than), ">" (greater than), "<=" (less than or equal to), ">=" (greater than or equal to), and "<>" (not equal to) to create more complex conditions.

sql
SELECT id, name, age
FROM employees
WHERE age BETWEEN 25 AND 35;

In the above query, the result set includes rows where the age falls between 25 and 35, inclusive.

The WHERE clause is a powerful tool for filtering data in SQL queries, allowing you to retrieve specific information based on defined conditions. It enables you to perform targeted operations on your data and retrieve only the relevant subset for analysis or further processing.