A WHERE clause filters data that meet some criteria.
WHERE only returns the rows you're interested in.
A WHERE condition returns either true or false.
WHERE can be used with SELECT, UPDATE, and DELETE.
List all suppliers in France.
SELECT * FROM Supplier WHERE Country = 'France'
Syntax of WHERE on a SELECT statement.
SELECT column-names FROM table-name WHERE condition
Syntax of WHERE on an UPDATE statement.
UPDATE table-name SET column-name = value WHERE condition
Syntax of WHERE on a DELETE statement.
DELETE table-name WHERE condition
SELECT Id, FirstName, LastName, City, Country, Phone FROM Customer WHERE Country = 'Sweden'
|5||Christina||Berglund||Luleå||Sweden||0921-12 34 65|
|24||Maria||Larsson||Bräcke||Sweden||0695-34 67 21|
UPDATE Supplier SET City = 'Sydney' WHERE CompanyName = 'Pavlova, Ltd.'
DELETE FROM Product WHERE UnitPrice > 50
Note: Referential integrity may prevent this deletion.
A better approach may be to discontinue the product, that is, set the column IsDiscontinued to true.
Be sure that the columns included in the WHERE clause are properly indexed.
If not, a table scan is performed which, with large tables, can be very slow.
Note: A table scan is an operation in which each table record is read to check if there is a match with the WHERE clause.