Slide 7.9: SQL select distinct statement
Slide 7.11: SQL update statement
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SQL Where Clause

The where clause is used to filter records. It is used to extract only those records that fulfill a specified criterion.

With the where clause, the operators below can be used: 
 SELECT  column_name(s)  FROM  table_name
   WHERE  column_name operator value

Operator Description Operator Description Operator Description
= Equal <> or != Not equal > Greater than
< Less than >= Greater than or equal <= Less than or equal
LIKE Search for a pattern BETWEEN Between an inclusive range IN One of the multiple vluaes

P_Id LastName FirstName Address City
1 Hansen Ola Timoteivn 10 Sandnes
2 Svendson Tove Borgvn 23 Sandnes
3 Pettersen Kari Storgt 20 Stavanger

To select only the persons living in the city Sandnes, we add a where clause to the select statement: 

 SELECT  *  FROM  Persons  WHERE  City = 'Sandnes';

 P_ID       LASTNAME      FIRSTNAME            ADDRESS          CITY
 --------   -----------   -----------------    -------------    -----------
 1          Hansen        Ola                  Timoteivn 10     Sandnes
 2          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. 

 SELECT  *  FROM  Persons  WHERE  FirstName=Tove;
 ERROR 1064 (42000): Syntax error near '=Tove' at line 1

 SELECT  *  FROM  Persons  WHERE  Year='1965';
 ERROR 1064 (42000): Syntax error near '=1965' at line 1


Demonstration
The following is an SQL test area from W3Schools, which uses the well-known Northwind sample database and the tables are for read only.
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SQL Statement:

Edit the SQL statement and click     to see the result, or    

Result:

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The menu to the right displays the database, and will reflect any changes.
Feel free to experiment with any SQL statement.
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The Database includes:
The Database includes:

TablenamesRecords
Customers91
Categories8
Employees10
OrderDetails518
Orders196
Products77
Shippers3
Suppliers29