The primary condition is that It can’t be null. The primary key is used to identify data uniquely therefore two rows of a table can’t have the same primary key values. While working with relational database management systems, the keys are the most important aspect to maintaining the relationship between two tables or uniquely identifying data or records from the database tables. Read More Articles Related to SQL Server Summary IDENTITY NOT NULL, NULL,ĬONSTRAINT PRIMARY KEY NONCLUSTERED (),ĬONSTRAINT FOREIGN KEY () REFERENCES. = 'parent')ĬONSTRAINT PRIMARY KEY NONCLUSTERED () is what would be referred to as an "orphan record". Having a null foreign key is usually a bad idea. This is easy to accomplish using a clustered index. What's the advantage? If you are selecting the parent plus all child records, you want the child records next to each other. There are actually advantages to having a foreign key be supported with a clustered index, but you get only one per table. You must manually create an index on foreign keys. Defining Primary key and Foreign key -Create Parent TableĭeptID int PRIMARY KEY, -define primary keyĮmpID int PRIMARY KEY, -define primary keyĭeptID int FOREIGN KEY REFERENCES Department(DeptID)Īs Jellinek suggested, I would like to add the below points about the foreign keys:įoreign keys do not automatically create an index, clustered or non-clustered. We can have more than one foreign key on a table. Exception Handling in SQL Server by TRY…CATCH.Different Types of stored procedure sql Server.Definition, Use of Group by and Having Clause.Different Types of Triggers In SQL Server.Create a comma separated list from column using select statement.Delete Duplicate Rows in SQL Server From a Table.Remove unsent database email from SQL Server.Get nth highest and lowest salary of an employee.Get field name, data type and size of database table.Difference between Stored Procedure and Function in SQL Server.Inserted, Logical Deleted table in SQL Server,.Drop all tables, stored procedure, views and triggers.Swap the values of two columns in SQL Server.Clear List of Recent SQL Server Connection From SQL Server Management Studio.How to insert values to identity column in SQL Server.Calculate Running Total, Total of a Column and Row.Understanding SQL Server Case Expression with Example.Difference between CTE and Temp Table and Table Variable.Difference between Primary Key and Unique Key.SQL Integrity Constraints or Constraints.Different Types of SQL Server Functions.Difference between inner join and equi join and natural join.Difference between Primary Key and Foreign Key.JavaScript ES6 Interview Questions Answers BookĪSP.NET Web API Questions and Answers Book NET Framework Questions and Answers BookĪSP.NET and AJAX Questions and Answers BookĮntity Framework 6.x Questions and Answers BookĮntity Framework Core Questions and Answers BookĪzure Administrator Questions and Answers BookĪzure Developer Questions and Answers Book NET Design Patterns Questions and Answers Book
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