Understanding Condition Statements in SQL
Daniel Hayes
Full-Stack Engineer · Leapcell

Key Takeaways
- Condition statements filter and control data in SQL queries.
- Common statements include WHERE, CASE, and HAVING.
- Proper use improves query accuracy and efficiency.
SQL (Structured Query Language) is widely used for managing and manipulating relational databases. One of the core functionalities of SQL is the ability to filter, select, and manipulate data based on specific conditions. This is achieved using condition statements. In this article, we will explore what condition statements are in SQL, their types, and how they are used in various scenarios.
What Are Condition Statements in SQL?
Condition statements in SQL are expressions that evaluate to either TRUE
, FALSE
, or UNKNOWN
. They are used to filter records, control the flow of queries, and make decisions within SQL scripts. These statements often appear in clauses such as WHERE
, HAVING
, and in control-of-flow constructs like CASE
and IF
.
Common Types of Condition Statements
1. The WHERE Clause
The WHERE
clause is the most commonly used condition statement in SQL. It filters records returned by a query based on a specified condition.
Example:
SELECT * FROM employees WHERE department = 'Sales';
This statement retrieves all employees who work in the Sales department.
2. Logical Operators
SQL supports logical operators to combine multiple conditions:
AND
: All conditions must be true.OR
: At least one condition must be true.NOT
: Negates a condition.
Example:
SELECT * FROM employees WHERE department = 'Sales' AND salary > 50000;
This returns employees in the Sales department with a salary greater than 50,000.
3. The CASE Statement
The CASE
statement is SQL's way to implement conditional logic inside queries. It works like an IF-THEN-ELSE
statement in programming languages.
Example:
SELECT name, salary, CASE WHEN salary > 70000 THEN 'High' WHEN salary BETWEEN 50000 AND 70000 THEN 'Medium' ELSE 'Low' END AS salary_grade FROM employees;
This adds a column salary_grade
based on the value of salary
.
4. IF Statement (in Stored Procedures)
Some database systems like MySQL support the IF
statement inside stored procedures.
Example:
IF salary > 50000 THEN SET bonus = 1000; ELSE SET bonus = 500; END IF;
5. The HAVING Clause
The HAVING
clause is used to filter groups after aggregation, similar to how WHERE
filters rows before aggregation.
Example:
SELECT department, COUNT(*) FROM employees GROUP BY department HAVING COUNT(*) > 10;
This returns only departments with more than 10 employees.
Using Comparison Operators
Condition statements often use comparison operators, such as:
=
(equal)!=
or<>
(not equal)>
(greater than)<
(less than)>=
(greater than or equal to)<=
(less than or equal to)BETWEEN
IN
LIKE
IS NULL
Example:
SELECT * FROM employees WHERE hire_date BETWEEN '2022-01-01' AND '2022-12-31';
Best Practices
- Use parentheses to clarify precedence in complex conditions.
- Be aware of NULL values: comparisons with
NULL
using=
or<>
will returnUNKNOWN
. UseIS NULL
orIS NOT NULL
instead. - Avoid unnecessary complexity: Write clear, readable conditions.
Conclusion
Condition statements are an essential part of writing effective SQL queries. They allow you to retrieve, manipulate, and analyze data with precision. By mastering condition statements—such as WHERE
, HAVING
, and CASE
—you can write powerful queries to handle complex data requirements.
FAQs
It is an expression used to filter or control data in a query.
The WHERE clause is most commonly used.
It enables precise data retrieval and analysis.
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