SQL SET Keyword

The SET keyword in SQL is used within the UPDATE statement to specify the new values for the columns you want to modify in a table.

SET: Definition and Usage

The SET clause comes after the UPDATE keyword and before the WHERE clause (if you're updating specific rows). It's crucial for defining which columns are being changed and to what new values.

Important Note about WHERE Clauses

Always, always use a WHERE clause with your UPDATE statements! If you omit the WHERE clause, the UPDATE statement will modify *every single row* in the table. This can lead to significant data loss if not handled carefully.

Syntax

UPDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition;
      

Examples

Updating a Specific Row

This updates the 'ContactName' and 'City' for the customer with 'CustomerID' = 1.

UPDATE Customers
SET ContactName = 'Alfred Schmidt', City = 'Frankfurt'
WHERE CustomerID = 1;
      

(The row for CustomerID 1 in the Customers table will be updated)
      

Updating Multiple Rows

This updates the 'ContactName' for all customers from Mexico.

UPDATE Customers
SET ContactName = 'Juan'
WHERE Country = 'Mexico';
      

(Multiple rows in the Customers table will be updated)