ภาษา sql ยูนิคอลัมน์

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distincct ภาษา sql

SELECT DISTINCT column1, column2, ...

 FROM table_name; 
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ยูนิค constraint mssql

USE AdventureWorks2012;  
GO  
CREATE TABLE Production.TransactionHistoryArchive4  
 (  
   TransactionID int NOT NULL,   
   CONSTRAINT AK_TransactionID UNIQUE(TransactionID)   
);   
GO  

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ภาษา sql พิเศษ

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);
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ตั้งค่าคอลัมน์ที่พิเศษในภาษา sql เซิร์ฟเวอร์

ALTER TABLE Persons
ADD UNIQUE (ID);

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