SQL DISTINCT Keyword
SQL DISTINCT returns unique records from a table in the SQL database.
By default SQL queries return all rows, including duplicate records. The SQL DISTINCT
keyword is used to eliminate duplicate records in the result set and display a distinct
list of values.
The SQL DISTINCT Keyword Syntax
The general syntax for a simple SQL Distinct is below. It
returns only DISTINCT (different) values by eliminate duplicates in the result
set.
SELECT DISTINCT column-names
FROM
table-name;
DISTINCT Keyword Practical Examples
SQL DISTINCT On One Column
Below DISTINCT Statement will return single Column
[FirstName] from [Employees] table.
SELECT
DISTINCT [FirstName]
FROM
[Employees];
SQL DISTINCT Multiple Columns
Below Distinct Statement will return multiple Columns
[FirstName], [LastName] from [Employees] table.
SELECT DISTINCT [FirstName], [LastName],
FROM [Employees];
SQL DISTINCT Statement on All Columns
If used (*) instead of column name in SQL Statement it will
return all DISTINCT rows from [Employees] table.
SELECT DISTINCT (*)
FROM [Employees];
Caution: It’s not ideal select all columns all the
time if only need certain columns as that increase burden on SQL engine. We
will discuss its effects on another day!
SQL DISTINCT and WHERE Clause
The following will list the DISTINCT employees and limit the
result set to the Where Clause
SELECT
DISTINCT [FirstName]
FROM
[Employees];
WHERE FirstName= ='David';
SQL DISTINCT Count
When SQL COUNT () used with DISTINCT it eliminate the duplicate records of
the same data and only count distinct records once.
SELECT
COUNT (DISTINCT
[FirstName])
FROM
[Employees];
SQL DISTINCT and NULL Values
SQL DISTINCT eliminate the duplicate records of the Null
data and only count single Null record.
