SQL Unique Constraint - Unique Key in SQL - Create Unique Constraints SQL Server
SQL UNIQUE Constraint
- UNIQUE is like making sure everyone in a group has a different name.
- PRIMARY KEY is like having a special leader in the group, and everyone's name must be unique, just like the UNIQUE rule.
UNIQUE Constraint on CREATE TABLE
Syntax
CREATE TABLE tbl_Wikitechy ( ID INT NOT NULL UNIQUE, student_Name VARCHAR(50) NOT NULL, Mark INT, Age INT )
Output
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UNIQUE Constraint on ALTER TABLE
- To establish a UNIQUE constraint on the 'ID' column after the table is already created, use the following SQL
Syntax
ALTER TABLE tbl_Wikitechy ADD UNIQUE (ID);
Output
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- To assign a name to a UNIQUE constraint and define it on multiple columns, use the following SQLsyntax
Syntax
ALTER TABLE tbl_Wikitechy ADD CONSTRAINT PK_Person UNIQUE (Id);
Output
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DROP a UNIQUE Constraint
- To remove a UNIQUE constraint, utilize the following SQL
Syntax
ALTER TABLE tbl_Wikitechy DROP CONSTRAINT PK_Person;
Output
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