sql where

The SQL WHERE clause is used to filter records in a database query, allowing you to retrieve only those rows that meet specific conditions. It is commonly used with SELECT, UPDATE, and DELETE statements to specify which records should be affected or returned

Key Points about the SQL WHERE Clause

• Purpose : Filters rows based on a condition or set of conditions.

• Syntax :

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

• Conditions : Can use comparison operators (=, <, >, <=, >=, <>), logical operators (AND, OR, NOT), and special operators like LIKE, IN, BETWEEN, IS NULL

• Text vs Numeric : Text values in conditions require single quotes, numeric values do not

• Multiple Conditions : Use AND to require all conditions to be true, or OR to require any condition to be true

• Performance : Using IN with a list of values is generally faster and cleaner than multiple OR conditions on the same field

Examples

• Select customers from Mexico with salary above 2000:

  sql
  
  SELECT ID, NAME, SALARY FROM CUSTOMERS WHERE Country = 'Mexico' AND SALARY > 2000;
  

• Select customers whose name is either Khilan, Hardik, or Muffy:

  sql
  
  SELECT * FROM CUSTOMERS WHERE NAME IN ('Khilan', 'Hardik', 'Muffy');
  

• Select customers from Spain whose name starts with 'G':

  sql
  
  SELECT * FROM Customers WHERE Country = 'Spain' AND CustomerName LIKE 'G%';
  

The WHERE clause is supported by all major SQL databases such as MySQL, PostgreSQL, Oracle, SQL Server, SQLite, and others, making it a fundamental tool for querying and manipulating data efficiently

. In summary, the WHERE clause is essential for filtering data in SQL queries by specifying conditions that rows must satisfy to be included in the results or affected by data modification statements