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:
Name | Description |
---|---|
column_name | Name of the column. |
table_name | Name of the table. |
conditions | It may be a condition, a select query or an expression. |
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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