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why to create unique constraints in sql

Anna Helena Drumond answered on October 21, 2022 Popularity 9/10 Helpfulness 4/10

answer why to create unique constraints in sql

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)
);

Popularity 9/10 Helpfulness 4/10 Language typescript

Source: Grepper

Tags: sql typescript

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Contributed on Oct 21 2022

Anna Helena Drumond

0 Answers Avg Quality 2/10

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