sql select unique
SELECT DISTINCT column1, column2, ...
FROM table_name;
sql unique
-- To name a UNIQUE constraint, and to define a UNIQUE constraint on
-- multiple columns, use the following SQL syntax:
-- MySQL / SQL Server / Oracle / MS Access:
CREATE TABLE Persons (
ID int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int,
CONSTRAINT UC_Person UNIQUE (ID,LastName)
);
DISTINCT SQL
SELECT DISTINCT column1, column1, ..... FROM TABLE
/*DISTINCT WILL NOT SELECT THE SAME VALUES IN SAME COLUMN*/
unique constraint mssql
USE AdventureWorks2012;
GO
CREATE TABLE Production.TransactionHistoryArchive4
(
TransactionID int NOT NULL,
CONSTRAINT AK_TransactionID UNIQUE(TransactionID)
);
GO
sql unique
This constraint ensures all values in a column are unique.
Example 1 (MySQL): Adds a unique constraint to the id column when
creating a new users table.
CREATE TABLE users (
id int NOT NULL,
name varchar(255) NOT NULL,
UNIQUE (id)
);
Example 2 (MySQL): Alters an existing column to add a UNIQUE
constraint.
ALTER TABLE users
ADD UNIQUE (id);
adding unique constraint in sql
ALTER TABLE Persons
ADD UNIQUE (ID);
