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20 Οκτ 2008 · You can only have one primary key, but you can have multiple columns in your primary key. You can also have Unique Indexes on your table, which will work a bit like a primary key in that they will enforce unique values, and will speed up querying of those values.
To allow naming of a PRIMARY KEY constraint, and for defining a PRIMARY KEY constraint on multiple columns, use the following SQL syntax: MySQL / SQL Server / Oracle / MS Access: ALTER TABLE Persons
18 Απρ 2024 · In Table Designer, select the row selector for the database column you want to define as the primary key. If you want to select multiple columns, hold down the CTRL key while you select the row selectors for the other columns. Right-click the row selector for the column and select Set Primary Key.
22 Ιουλ 2024 · When you specify a primary key constraint for a table, the Database Engine enforces data uniqueness by automatically creating a unique index for the primary key columns. This index also permits fast access to data when the primary key is used in queries.
10 Σεπ 2011 · The first common option is to define an integer column as a primary key. You can have your application assign a value or you can assign an identity property to the integer column (i.e. int identity (1,1)) and let SQL Server generate the value for you (which is my preference).
CREATE TABLE tablename (column1 DATATYPE, column2 DATATYPE, …………………………………, CONSTRAINT constraint_name PRIMARY KEY (column1, column2)); Alter Table Syntax. ALTER TABLE tablename ADD PRIMARY KEY (columnname); ALTER TABLE tablename ADD CONSTRAINT constraint_name PRIMARY KEY (column1, column2); Drop Table Syntax
22 Φεβ 2022 · Create Primary Key on Multiple Columns in SQL Server. Primary Key During the Table Creation. Primary Key After the Table Creation. Drop the Primary Key in SQL Server. Modify the Primary Key. Disable/Enable Primary Key. The Myths about the Primary Key. Table with Primary Key is not a Heap Table.
