The WHERE Clause

The WHERE clause is used to specify a selection criterion.

To conditionally select data from a table, a WHERE clause can be added to the SELECT statement. 
 SELECT  column  FROM  table
   WHERE  column operator value

With the WHERE clause, the following operators can be used:

Operator Description Operator Description Operator Description
= Equal <> Not equal > Greater than
< Less than >= Greater than or equal <= Less than or equal
BETWEEN Between an inclusive range LIKE Search for a pattern

Using the WHERE Clause
To select only the persons living in the city “Sandnes”, we add a WHERE clause to the SELECT statement:

LastName FirstName Address City
Hansen Ola Timoteivn 10 Sandnes
Svendson Tove Borgvn 23 Sandnes
Pettersen Kari Storgt 20 Stavanger
Rasmussen   Storgt 67   

 SQL> select  *  from  Persons  where  City = 'Sandnes';

 LASTNAME       FIRSTNAME             ADDRESS           CITY
 ------------   ------------------    --------------    ------------
 Hansen         Ola                   Timoteivn 10      Sandnes
 Svendson       Tove                  Borgvn 23         Sandnes

Single quotes are used around the conditional values in the examples. SQL uses single quotes around text values (most database systems also accept double quotes). Numeric values should not be enclosed in quotes.

The following is an SQL test area from w3schools.com where the Customers table may be created by the following command: 
   SQL> create table  Customers (
     2    CustomerID   varchar(16),
     3    CompanyName  varchar(32), 
     4    ContactName  varchar(32),
     5    Address      varchar(64),
     6    City         varchar(32), 
     7    PostalCode   varchar(16), 
     8    Country      varchar(32) );
Note that the Customers table is for read only.

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