Sql unique

This article is tagged with: Sql unique and mysql

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);

This article is tagged with: Sql unique and mysql