WHERE Condition in SQL

WHERE Condition in SQL

WHERE Condition in SQL

The WHERE condition in SQL is an essential clause used to filter records based on a specified condition. It helps retrieve only those rows that meet the defined criteria, ensuring precise data extraction. Whether used in a SELECT, UPDATE, or DELETE statement, the WHERE condition plays a crucial role in database operations by applying filters to retrieve only relevant records.

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Understanding the WHERE Condition

The WHERE condition is used when fetching data from a single table or multiple joined tables. If the given condition is met, only the qualifying rows are returned. This helps in extracting accurate data while optimizing database queries efficiently.

Syntax of WHERE Condition

SELECT column1, column2, ..... columnN  
FROM table_name  
WHERE {condition};  

Key Points About WHERE Condition:

  • The WHERE condition is not limited to the SELECT statement; it is also used with UPDATE and DELETE statements.
  • It supports various comparison and logical operators such as =, >, <, LIKE, NOT, BETWEEN, IN, etc.
  • It is case-sensitive in some databases and requires exact string matches within single quotes ('').


Example of WHERE Condition in SQL

Let’s consider a sample table named EMPLOYEES, which contains employee details:

EmployeeID EmployeeName Department Age Salary
101 Aryan Sharma IT 27 55000.00
102 Meera Raj HR 30 62000.00
103 Sohan Verma Finance 28 48000.00
104 Kiran Das Marketing 32 72000.00
105 Rohan Mehta IT 26 51000.00

Fetching Employees with Salary Greater than 50,000

To retrieve EmployeeID, EmployeeName, and Salary for employees earning more than 50,000, we use the following query:

SELECT EmployeeID, EmployeeName, Salary  
FROM EMPLOYEES  
WHERE Salary > 50000;  

Output:

EmployeeID EmployeeName Salary
101 Aryan Sharma 55000.00
102 Meera Raj 62000.00
104 Kiran Das 72000.00
105 Rohan Mehta 51000.00


Fetching Employee Details by Name

If we need to find details of a specific employee, such as Sohan Verma, we can use the following query:

SELECT EmployeeID, EmployeeName, Salary  
FROM EMPLOYEES  
WHERE EmployeeName = 'Sohan Verma';  

Output:

EmployeeID EmployeeName Salary
103 Sohan Verma 48000.00

Important Notes:

  • String values should always be enclosed in single quotes (').
  • Numeric values do not require quotes.
  • The WHERE condition can be combined with logical operators like AND, OR, and NOT for more complex filtering.

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Conclusion

The WHERE condition in SQL is a fundamental clause that helps filter data efficiently. Whether retrieving specific records, updating certain values, or deleting unwanted data, the WHERE clause ensures accuracy in database queries. Mastering this concept is crucial for anyone working with SQL databases.

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