SQL UPDATE Statements - MSDN Documentation

SQL UPDATE Statement

The UPDATE statement is used to modify existing records in a table. It allows you to change the values of one or more columns in rows that meet specific criteria.

Syntax

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

Parameters

table_name: The name of the table you want to update.
column1, column2, ...: The names of the columns you want to update.
value1, value2, ...: The new values to assign to the specified columns. These can be literal values, expressions, or even values from other columns.
WHERE condition: (Optional) A condition that specifies which rows to update. If the WHERE clause is omitted, all rows in the table will be updated.

Examples

Example 1: Update a single column for a specific record

This example updates the Email of a customer with CustomerID 10.

UPDATE Customers
SET Email = 'new.email@example.com'
WHERE CustomerID = 10;

Example 2: Update multiple columns for multiple records

This example increases the DiscountPercentage by 5% for all customers in 'USA' and updates their ModifiedDate.

UPDATE Customers
SET DiscountPercentage = DiscountPercentage + 0.05,
    ModifiedDate = GETDATE()
WHERE Country = 'USA';

Example 3: Update a column based on another table (using a subquery)

This example updates the StockQuantity in the Products table based on the total quantity ordered in the OrderDetails table.

UPDATE Products
SET StockQuantity = StockQuantity - (
    SELECT SUM(Quantity)
    FROM OrderDetails
    WHERE OrderDetails.ProductID = Products.ProductID
)
WHERE EXISTS (
    SELECT 1
    FROM OrderDetails
    WHERE OrderDetails.ProductID = Products.ProductID
);

Important Considerations

Always use a WHERE clause unless you explicitly intend to update every row in the table. Omitting the WHERE clause can lead to unintended data loss or modification.
Backup your data before performing any significant UPDATE operations.
Test your UPDATE statements on a development or staging environment before running them on production.
Understand the data types of the columns you are updating to ensure compatibility with the new values.

MSDN Documentation

SQL Server Documentation