It is like a Primary key but it can accept only one null value and it can not have duplicate values.Ī set of one or more table fields or the column that uniquely identifies a specific record in a table is known as a "unique key" constrain. ) Primary key constraint at table level ALTER TABLE table_nameĪDD PRIMARY KEY (col1,col2)Ī unique key is a set of one or more fields/columns of a table that uniquely identify each record/row in a database table. Primary key constraint at column level CREATE TABLE table_nameĬol1 datatype PRIMARY KEY, By doing all these, it creates a composite primary key when the multiple fields are used as the primary key Any table may only have a single primary key, that can be made up of one or multiple fields. By default with the primary key, null values are not allowed in a primary key column of the table. The primary keys must have distinct values which means one of the columns of the table should have a unique value from the other. And at the same time, the primary key is also one type of integrity constraint ultimately. The primary key is a field of a database table that is used to uniquely identifies every record or the table row. It can not accept null, duplicate values. The primary key is a set of one or more fields/columns of a table that uniquely identify each record/row in the database table. In Microsoft SQL Server we have six types of constraints The constraints can be specified after all the columns are defined with the ALTER TABLE statement. These are called column-level constraints. The constraints can be specified immediately after the column definition with the CREATE TABLE statement. The table-level Integrity constraints apply to the entire table, while the column level constraints are only applied to one column. We can apply the integrity constraints at the column or table level. Achieving the complete configuration of the constraints ensures that the data in the database is accurate and reliable to be consumed in the application. Constrains are generally used to restrict the multiple types of information that can be entered into a table to ensure the integrity of the data. The integrity constraints are one of the protocols that should be followed by the table's data columns. Basically, constraints are used to restrict the type of data that can insert into a database table. Exception Handling in SQL Server by TRY…CATCHĬonstraints are some rules that enforce on the data to be entered into the database table.
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.
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