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How to retrieve a primary key in SQL Server?
The sys.key_constraints system view contains a row for each object that is a primary key or unique constraint. Therefore we could use the following code to return all primary key constraints in the database, along with the relevant table for each primary key: Of course, you can remove the WHERE clause to return both primary keys and unique keys.
How to find an array of primary key values?
An array of primary key values to find. The type of the array is Object. A DataRow object that contains the primary key values specified; otherwise a null value if the primary key value does not exist in the DataRowCollection. No row corresponds to that index value. The table does not have a primary key.
How to find the primary key in a datarow?
A DataRow that contains the primary key value specified; otherwise a null value if the primary key value does not exist in the DataRowCollection. The table does not have a primary key. The following example uses the Find method to find the primary key value “2” in a collection of DataRow objects.
What happens when two rows have the same primary key?
When two or more rows have the same primary key value, then the first row found is returned. This occurs when EnforceConstraints is set to false. See the PrimaryKey property for more information about how to create a PrimaryKey column, or an array of DataColumn objects when the table has more than one primary key.
How to list all primary keys in DB2 database?
Query below lists all primary keys constraints ( PK) in the database with their columns (one row per column). See also: list of all primary keys (one row per PK). Get this interactive HTML data dictionary in minutes with Dataedo.
How to get the primary key for a table?
If you just want the primary key for a given table, the sp_pkeys system stored procedure is probably the quickest and easiest way to do it. To do this, simply pass the table name to the procedure. Result (using vertical output):
How to get primary key from artists table?
In this case I requested the primary key from the Artists table. It returns the primary key name ( PK__Artists__25706B50FCD918B1 ), the database name ( Music ), the table name, the column name ( ArtistId ), plus other information. Alternatively, I could have explicitly specified all arguments to get the same result:
When to use a two column primary key?
This occurs when a single column can’t contain enough unique values. For example, a two column primary key might consist of a “FirstName” and “LastName” column. Because primary keys can be made up of more than one column, the PrimaryKey property consists of an array of DataColumn objects.
What makes a table extension a secondary key in SQL?
In SQL, table extension objects inherit the primary key of the table object they extend (the base table object). So any key that you define in a table extension object is considered a secondary key. Secondary keys create indexes in SQL.
How to define primary key for a table?
CREATE TABLE languages ( language_id INTEGER , name TEXT NOT NULL , PRIMARY KEY (language_id) ); However, for tables that the primary keys consist of more than one column, you must use PRIMARY KEY table constraint to define primary keys. The following statement creates the country_languages table whose primary key consists of two columns.