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SQL UNIQUE Constraint

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SAMER SAEID answered on January 7, 2021 Popularity 10/10 Helpfulness 3/10

answer SQL UNIQUE Constraint

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SQL UNIQUE Constraint

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CREATE TABLE Colleges (
  college_id INT NOT NULL UNIQUE,
  college_code VARCHAR(20) UNIQUE,
  college_name VARCHAR(50)
);

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Contributed on May 22 2022

SAMER SAEID

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why to create unique constraints in sql

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The following SQL creates a UNIQUE constraint on the "ID" column when the "Persons" table is created:
CREATE TABLE Persons (
    ID int NOT NULL UNIQUE,
    LastName varchar(255) NOT NULL,
    FirstName varchar(255),
    Age int
);

MySQL:

CREATE TABLE Persons (
    ID int NOT NULL,
    LastName varchar(255) NOT NULL,
    FirstName varchar(255),
    Age int,
    UNIQUE (ID)
);

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)
);

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Contributed on Oct 21 2022

Anna Helena Drumond

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sql unique

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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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Contributed on Jan 07 2021

Lorenzo Satta Chiris

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unique sql

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CREATE TABLE order_details
( order_detail_id integer CONSTRAINT order_details_pk PRIMARY KEY,
  order_id integer NOT NULL,
  order_date date,
  quantity integer,
  notes varchar(200),
  CONSTRAINT order_unique UNIQUE (order_id)
);

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Source: www.techonthenet.com

Tags: sql

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Contributed on Jul 04 2022

Goutam De

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SQL UNIQUE Constraint

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