The page explains the SQL UPDATE statement—a command in SQL used to modify existing records in a table.

• UPDATE Syntax:

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

  The WHERE clause is crucial; if omitted, all records in the table will be updated.

• Example:
  Updates the contact name and city for a customer with CustomerID = 1:

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

• Multiple Record Update:
  You can update multiple records by changing the WHERE condition, e.g., updating all customers in "Mexico":

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

• Warning:
  If the WHERE clause is left out, every row in the table will be changed.

• Summary:

  • The UPDATE statement modifies data in a table.
  • Always use a WHERE clause to avoid accidental mass updates.
  • The page provides practical table examples and a practice question about the command’s purpose.

This serves as a practical guide and warning for safe and accurate data updates in SQL tables.[1]

1

SQL UPDATE Statement

The SQL UPDATE Statement

The UPDATE statement is used to modify the existing records in a table.

UPDATE Syntax

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

Note: Be careful when updating records in a table! Notice the WHERE clause in the UPDATE statement. The WHERE clause specifies which record(s) that should be updated. If you omit the WHERE clause, all records in the table will be updated!

Demo Database

Below is a selection from the Customers table used in the examples:

UPDATE Table

The following SQL statement updates the first customer (CustomerID = 1) with a new contact person and a new city.

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

The selection from the "Customers" table will now look like this:

UPDATE Multiple Records

It is the WHERE clause that determines how many records will be updated.

The following SQL statement will update the ContactName to "Juan" for all records where country is "Mexico":

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

The selection from the "Customers" table will now look like this:

Update Warning!

Be careful when updating records. If you omit the WHERE clause, ALL records will be updated!

UPDATE Customers  
SET ContactName='Juan';