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The ADD CONSTRAINT command is used to create a constraint after a table is already created. The following SQL adds a constraint named "PK_Person" that is a PRIMARY KEY constraint on multiple columns (ID and LastName):
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29 Ιουν 2023 · ADD CONSTRAINT is a SQL command that is used together with ALTER TABLE to add constraints (such as a primary key or foreign key) to an existing table in a SQL database. The basic syntax of ADD CONSTRAINT is:
In SQL, we can add rules for a column while inserting new values in a table. In this tutorial, you will learn about constraints in SQL with the help of examples.
To add a unique constraint, you use the ALTER TABLE statement with the ADD keyword and the UNIQUE keyword. ALTER TABLE TableName ADD CONSTRAINT UQ_TableName_ColumnName UNIQUE (ColumnName); Check Constraint. A check constraint enforces a condition that values in a column must satisfy.
11 Σεπ 2023 · Here we will see how to add unique key constraint to a column(s) of a MS SQL Server's database with the help of a SQL query using ALTER clause. For the demonstration purpose, we will be creating a demo table in a database called "geeks".
15 Σεπ 2020 · Managing Constraints. In MySQL, you can add constraints to existing tables as well as delete them with ALTER TABLE statements. For example, the following command adds a UNIQUE constraint to the empName column in the employeeInfo table created previously:
11 Οκτ 2022 · Constraints in SQL are helpful to ensure your data remains high quality. There are five different types of constraints you can use, which come in handy in different situations. When you design your database, work out the rules you need to enforce on your data, and create constraints on your tables.
