The SELECT statement is used to select data from a database.

1. SQL COMMANDS
DATABASE SYSTEM
ANGELO T. RETITA
IT-INSTRUCTOR

2. OBJECTIVES
■ 1. To understand the usage of SQL SELECT Statement.
■ 2. To determine the syntax of SQL SELECT Statement.
■ 3. To understand the usage of SQL SELECT DISTINCT Statement.
■ 4. To determine the syntax of SQL SELECT DISTINCT Statement.
■ 5. To understand the usage of SQL WHERE Clause.
■ 6. To determine the syntax of SQL WHERE Clause.

3. SQL SELECT Statement
■ The SELECT statement is used to select data from a database.
■ The data returned is stored in a result table, called the
■RESULT-SET

4. SELECT Syntax
■ SELECT column1, column2, ...
FROM table_name;
Here, column1, column2, ... are the field names of the table you want to select
data from. If you want to select all the fields available in the table, use the
following syntax:
■ SELECT * FROM table_name;

5. SELECT * Example
■ Example:
– 1. SELECT * FROM Customers;
Table Customers

6. SELECT Column Example
■ Example:
– 2. SELECT CustomerName, City FROM Customers;
Table Customers

7. SQL SELECT DISTINCT Statement
■ The SELECT DISTINCT statement is used to return only distinct (different) values.
■ Inside a table, a column often contains many duplicate values; and sometimes you
only want to list the different (distinct) values.

8. SELECT DISTINCT Syntax
■ SELECT DISTINCT column1, column2, ...
FROM table_name;

9. Example of SELECT DISTINCT
■ Below is a selection from the "Customers" table in the Northwind sample
database:
SELECT * FROM Customers;

10. Example 1.
■ A. The following SQL statement selects all (and duplicate) values from the
"Country" column in the "Customers" table:
■ B. The following SQL statement selects only the DISTINCT values from the
"Country" column in the "Customers" table:
A. SELECT Country FROM Customers; B. SELECT DISTINCT Country FROM Customers;

11. Example of SELECT DISTINCT Count
■ The following SQL statement lists the number of different (distinct) customer
countries:
SELECT Count(*) AS DistinctCountries
FROM (SELECT DISTINCT Country FROM Customers);
SELECT DISTINCT Country
FROM Customers;

12. SQL WHERE
Clause

13. SQL WHERE Clause
■ The WHERE clause is used to filter records.
■ The WHERE clause is used to extract only those records that fulfill a specified
condition.

14. WHERE Syntax
SELECT column1, column2, ...
FROM table_name
WHERE condition;

15. Note!
The WHERE clause is not only used in SELECT
statement, it is also used in UPDATE, DELETE
statement, etc.!

16. Demo Database
■ Below is a selection from the "Customers" table in the Northwind sample
database:

17. WHERE Clause Example
■ The following SQL statement selects all the customers from the country "Mexico",
in the "Customers" table:
SELECT * FROM Customers
WHERE Country='Mexico';

18. Text Fields vs. Numeric Fields
■ SQL requires single quotes around text values (most database systems will also
allow double quotes).
■ However, numeric fields should not be enclosed in quotes:
Example
SELECT * FROM Customers
WHERE CustomerID=1;

19. Operators in The WHERE Clause
Operator Description
= Equal
<> Not equal. Note: In some versions of SQL this operator may be written as !=
> Greater than
< Less than
>= Greater than or equal
<= Less than or equal
BETWEEN Between an inclusive range
LIKE Search for a pattern
IN To specify multiple possible values for a column
The following operators can be used in the WHERE clause:

20. =(Equal) Operator in The WHERE
Clause Example
SELECT CustomerID, CustomerName, ContactName, Address, City, PostalCode, Country
FROM Customers
WHERE (CustomerName = 'Alfreds Futterkiste');
Filtering records having CustomerName EQUAL Alfreds Futterkiste.

21. <>(Not Equal) Operator in The WHERE
Clause Example
SELECT CustomerID, CustomerName, ContactName, Address, City, PostalCode, Country
FROM Customers
WHERE (CustomerName <> 'Alfreds Futterkiste');
Filtering records of CustomerName NOT EQUAL Alfreds Futterkiste.

22. < (Less than) Operator in The WHERE
Clause Example
SELECT CustomerID, CustomerName, ContactName, Address, City, PostalCode, Country
FROM Customers
WHERE (CustomerID < 2);
Filtering records having CustomerID LESS THAN 2.

23. >(Greater than) Operator in The
WHERE Clause Example
SELECT CustomerID, CustomerName, ContactName, Address, City, PostalCode,
Country
FROM Customers
WHERE (CustomerID > 2)
Filtering records having CustomerID GREATER THAN 2.

24. <=(Less than equal) Operator in The
WHERE Clause Example
SELECT CustomerID, CustomerName, ContactName, Address, City, PostalCode, Country
FROM Customers
WHERE (CustomerID <= 2)
Filtering records having CustomerID LESS THAN EQAL 2.

25. >=(Greater than equal) Operator in The
WHERE Clause Example
SELECT CustomerID, CustomerName, ContactName, Address, City, PostalCode, Country
FROM Customers
WHERE (CustomerID >= 2)
Filtering records having CustomerID GREATER THAN EQUAL 2.

26. BETWEEN Operator in The WHERE
Clause Example
SELECT CustomerID, CustomerName, ContactName, Address, City, PostalCode, Country
FROM Customers
WHERE (CustomerID BETWEEN 2 AND 4)
Filtering records of CustomerID BETWEEN 2 AND 4.

27. LIKE Operator in The WHERE Clause
Example
SELECT CustomerID, CustomerName, ContactName, Address, City, PostalCode, Country
FROM Customers
WHERE (CustomerName LIKE 'an%')
Filtering records of CustomerName LIKE an.

28. IN Operator in The WHERE Clause
Example
SELECT CustomerID, CustomerName, ContactName, Address, City, PostalCode, Country
FROM Customers
WHERE (CustomerID IN (1, 5))
Filtering records of CustomerID IN 1, 5.