In SQL Server (MS SQL), the DELETE query is used to remove rows from a table. Here’s a basic overview of how to use it:

Basic Syntax

Examples

1. Delete Specific Rows

   Suppose you have a table named Employees and you want to delete records for employees who are in the 'Sales' department.

   DELETE FROM Employees WHERE Department = 'Sales';

   This command will delete all rows where the Department column has the value 'Sales'.

2. Delete All Rows

   To delete all rows from a table but keep the table structure intact:

   DELETE FROM Employees;

   Be careful with this command, as it removes all data from the table.

3. Delete with Joins

   If you want to delete rows based on a condition involving another table, you can use a JOIN. For example, if you want to delete employees who belong to departments that are marked as inactive in another table called Departments:

   DELETE E FROM Employees E INNER JOIN Departments D ON E.DepartmentID = D.DepartmentID WHERE D.Status = 'Inactive';

   This command deletes rows from Employees where the corresponding department in Departments has a status of 'Inactive'.

Important Considerations

• Backup Data: Always ensure that you have a backup of your data before running a DELETE query, especially if it will affect a large number of rows.

• Transactions: You can use transactions to ensure that your DELETE operation is safe. For example:

  BEGIN TRANSACTION;
  DELETE FROM Employees WHERE Department = 'Sales';
  -- If everything looks good, commit the transaction
  COMMIT TRANSACTION;
  -- If something goes wrong, you can roll back the transaction -- ROLLBACK TRANSACTION;

• Foreign Key Constraints: Be aware of foreign key constraints that might prevent you from deleting rows if other tables depend on the rows you're trying to remove.