WHERE CLAUSE

The SQL WHERE clause allows to filtering of records in queries. Whether you’re retrieving data, updating records, or deleting entries from a database, the WHERE clause plays an important role in defining which rows will be affected by the query. Without it, SQL queries would return all rows in a table, making it difficult to target specific data.

In this article, we will learn the WHERE clause in detail—from basic concepts to advanced ones. We’ll cover practical examples, discuss common operators, provide optimization tips, and address real-world use cases.

What is the SQL WHERE Clause?

The SQL WHERE clause is used to specify a condition while fetching or modifying data in a database. It filters the rows that are affected by the SELECT, UPDATE, DELETE, or INSERT operations. The condition can range from simple comparisons to complex expressions, enabling precise targeting of the data.

Syntax:

SELECT column1,column2 FROM table_name WHERE column_name

operator value;

Parameter Explanation:

1. column1,column2: fields in the table

2. table_name: name of table

3. column_name: name of field used for filtering the data

4. operator: operation to be considered for filtering

5. value: exact value or pattern to get related data in the result 

Examples of WHERE Clause in SQL

We will create a basic employee table structure in SQL for performing all the where clause operation.

Query:

CREATE TABLE Emp1(    EmpID INT PRIMARY KEY,    Name VARCHAR(50),    Country VARCHAR(50),    Age int(2),  mob int(10));-- Insert some sample data into the Customers tableINSERT INTO Emp1 (EmpID, Name,Country, Age, mob)VALUES (1, 'Shubham',  'India','23','738479734'),       (2, 'Aman ',  'Australia','21','436789555'),       (3, 'Naveen', 'Sri lanka','24','34873847'),       (4, 'Aditya',  'Austria','21','328440934'),       (5, 'Nishant', 'Spain','22','73248679');

Output

Example 1: Where Clause with Logical Operators

To fetch records of  Employee with age equal to 24. 

Query:

SELECT * FROM Emp1 WHERE Age=24;

Output:

To fetch the EmpID, Name and Country of Employees with Age greater than 21. 

Query:

SELECT EmpID, Name, Country FROM Emp1 WHERE Age > 21;

Output:

Example 2: Where Clause with BETWEEN Operator

It is used to fetch filtered data in a given range inclusive of two values. 

Syntax: 

SELECT column1,column2 FROM table_name  WHERE column_name BETWEEN value1 AND value2;

Parameter Explanation:

1. BETWEEN: operator name 

2. value1 AND value2: exact value from value1 to value2 to get related data in result set.  

To fetch records of Employees where Age is between 22 and 24 (inclusive).

Query:

SELECT * FROM Emp1 WHERE Age BETWEEN 22 AND 24;

Output:

Example 3: Where Clause with LIKE Operator

It is used to fetch filtered data by searching for a particular pattern in the where clause. 

Syntax: 

SELECT column1,column2 FROM table_name WHERE column_name LIKE pattern;

Parameters Explanation:

1. LIKE: operator name 

2. pattern: exact value extracted from the pattern to get related data in the result set. 

Note: The character(s) in the pattern is case-insensitive.

To fetch records of Employees where Name starts with the letter S.

Query:

SELECT * FROM Emp1 WHERE Name LIKE 'S%'; 

The ‘%'(wildcard) signifies the later characters here which can be of any length and value. 

Output:

To fetch records of Employees where Name contains the pattern ‘M’.

Query:

SELECT * FROM Emp1 WHERE Name LIKE '%M%';

Output:

Example 4: Where Clause with IN Operator

It is used to fetch the filtered data same as fetched by ‘=’ operator just the difference is that here we can specify multiple values for which we can get the result set.

Syntax: 

SELECT column1,column2 FROM table_name WHERE column_name IN (value1,value2,..);

Parameters Explanation:

1. IN: operator name 

2. value1,value2,..: exact value matching the values given and get related data in the result set.

To fetch the Names of Employees where Age is 21 or 23.

Query:

SELECT Name FROM Emp1 WHERE Age IN (21,23);

Output:

List of Operators that Can be Used with WHERE Clause

Conclusion

The WHERE clause is use for filtering and refining SQL queries. Whether you’re working with basic conditions, using logical operators, or performing advanced queries with subqueries and EXISTS, mastering the WHERE clause is essential for every SQL user. Understanding how to efficiently filter data, avoid common pitfalls, and optimize your queries will ensure you’re able to write clean, fast, and accurate SQL queries.