SQL DISTINCT

Select with distinct

Redundancy is the repetition of certain data in a table. With the use of DISTINCT clause data redundancy may be avoided. This clause will eliminate the repetitive appearance of same data. DISTINCT can come only once in a given select statement.

Syntax:

SELECT DISTINCT <column_name> 
FROM <table_name> 
WHERE <conditions>;

Parameters:

Pictorial presentation :

Example-1: SQL DISTINCT

Sample table: orders

To get all 'agent_code' from the 'orders' table, the following SQL statement can be used:

SQL Code:

SELECT agent_code FROM orders;

Relational Algebra Expression:

Relational Algebra Tree:

Output:

AGENT_CODE
----------
A008
A004
A006
A010
A004
A011
A005
A013
A004
A005
A011

...
...

The above picture shows the same 'agent_code' appears more than once.

Example-2: SQL DISTINCT

To get each 'agent_code' once from the 'orders' table, the following SQL statement can be used :

SQL Code:

SELECT DISTINCT agent_code 
FROM orders;

Relational Algebra Expression:

Relational Algebra Tree:

Output:

AGENT_CODE
----------
A004
A002
A007
A009
A011
A012
A010
A013
A001
A008
A006
A005
A003

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