In SQL Server, you can use the TOP clause to limit the rows returned from a query to a certain percentage of the result set.
For example, you could return the top 10% of the results, or whatever percentage you need.
Author: Ian
Limit the Rows Returned in a SQL Server Query by using the TOP Clause
In SQL Server, you can use the TOP clause to limit the rows returned from a query result set. This clause provides similar functionality to LIMIT in MySQL, and ROWNUM in Oracle, although there are differences in how each of these work.
Below are examples of using the TOP clause to limit the result set in SQL Server.
Return All Foreign Keys & CHECK Constraints in a SQL Server Database (T-SQL Examples)
In SQL Server, you can use Transact-SQL to return a list of all foreign keys and CHECK constraints for the current database.
The examples on this page query two system views in order to retrieve this information: sys.foreign_keys and sys.check_constraints. You can query each one separately, or use UNION to display them all in a single result set.
Modify a CHECK Constraint in SQL Server using T-SQL
If you already have an existing CHECK constraint in SQL Server, but you need to modify it, you’ll need to drop it and recreate it. There’s no ALTER CONSTRAINT statement or anything similar.
So to “modify” an existing constraint:
- Drop the constraint using
ALTER TABLEwithDROP CONSTRAINT. - Create the new constraint using
ALTER TABLEwithADD CONSTRAINT.
Add a CHECK Constraint to an Existing Table in SQL Server (T-SQL)
This article demonstrates how to add a CHECK constraint to an existing table.
You can add a constraint to an existing table by using the ALTER TABLE statement along with the ADD CONSTRAINT argument. Examples below.
Rename a CHECK Constraint in SQL Server using T-SQL
You can use the sp_rename system stored procedure to rename a CHECK constraint in SQL Server.
The purpose of this stored procedure is to allow you to rename user-created objects in the current database. So you can also use it to rename other objects such as tables, columns, alias data types, etc.
Rename a Foreign Key in SQL Server using T-SQL
You can use the sp_rename system stored procedure to rename a foreign key constraint in SQL Server.
The purpose of this stored procedure is to allow you to rename user-created objects in the current database, so you can also rename other objects such as tables, columns, alias data types, etc.
How to Restore Trust in a Foreign Key Constraint in SQL Server (T-SQL Examples)
In SQL Server, a foreign key constraint (and a CHECK constraint) can be either trusted or not trusted.
When a constraint is trusted, this means that the constraint has been verified by the system. When it’s not trusted, the constraint has not been verified by the system.
Basically, when you have an untrusted constraint, you could also have invalid data in your database. By this I mean you could have data that violates the constraint.
This means that you’re no longer maintaining referential integrity within your relationships, which is not normally good practice when looking after a relational database in production.
In this article I’ll check my existing constraints for their “trustworthiness”, and then I’ll update them to become trustworthy once again.
How to Enable a Foreign Key Constraint in SQL Server (T-SQL Examples)
If you have a foreign key constraint in SQL Server that is currently disabled, you can use the code below to re-enable it.
When you enable a foreign key constraint, you have the option to specify whether or not to check any existing data in the table. This also applies when you enable a CHECK constraint.
Below are code examples of enabling a foreign key constraint, while specifying each of these different options.
How to Find All Constraint Violations in a SQL Server Database
You can run the DBCC CHECKCONSTRAINTS console command to return a list of all constraint violations in a SQL Server database.
This command checks the integrity of a specified constraint or all constraints on a specified table in the current database. It returns any foreign key and CHECK constraint violations that it finds.
You can use the ALL_CONSTRAINTS option to check both enabled and disabled constraints. If you omit this, then only enabled constraints are returned (unless you explicitly specify a constraint to check, in which case it will be returned regardless of whether it’s enabled or disabled).