Constraints in SQL Server are predefined rules that you can enforce on single or multiple columns. These constraints help maintain the integrity, reliability and accuracy of values stored in these columns. You
Integrity constraints in SQL are rules enforced on database tables to maintain data accuracy, consistency, and validity, such as ensuring unique primary keys and valid foreign key relationships.
According to the ANSI SQL standard, you can have multiple rows with NULL values for unique constraints. However, in SQL Server, you can use a NULL value only for a single row. You can use a NOT NULL constraint in addition to a unique constraint to address ...
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The constraints in the previous examples are column constraints. A table constraint is declared independently from a column definition and can apply to more than one column in a table. Table constraints must be used when more than one column must be included in a constraint. For example, if ...
The constraints in the previous examples are column constraints. A table constraint is declared independently from a column definition and can apply to more than one column in a table. Table constraints must be used when more than one column must be included in a constraint. For example, if ...
SQL Server supports the following classes of constraints: NOT NULL specifies that the column does not accept NULL values. For more information, seeAllowing Null Values. CHECK constraints enforce domain integrity by limiting the values that can be put in a column. For more information, seeCHECK C...
In order to follow this guide, you will need a computer running some type of relational database management system (RDBMS) that uses SQL. The instructions and examples in this guide were validated using the following environment: A server running Ubuntu 20.04, with a non-root user with adminis...
Examples A. Check a table The following example checks the constraint integrity of the tableTable1in theAdventureWorks2022database. SQL USEAdventureWorks2022; GOCREATETABLETable1 (Col1INT, Col2CHAR(30)); GOINSERTINTOTable1VALUES(100,'Hello'); GOALTERTABLETable1WITHNOCHECKADDCONSTRAINTchkTab1...
Examples See Also Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance Azure Synapse Analytics Analytics Platform System (PDW) Warehouse in Microsoft Fabric SQL database in Microsoft Fabric Contains a row for each object that is a default definition (created as part of a ...