How many primary keys are there in a single data table in the database

This article mainly introduces the number of primary keys in a single data table in the database, which is very detailed and has a certain reference value. Friends who are interested must read it all!

There can be only one primary key in a single data table in the database. Database primary key, refers to a column or a combination of columns, its value can uniquely identify each row in the table, through it can force the physical integrity of the table; the primary key is mainly associated with foreign keys of other tables, as well as the modification and deletion of this record.

There can be only one primary key in a single data table in the database.

A database primary key refers to a combination of columns or columns whose value uniquely identifies each row in the table, through which the physical integrity of the table can be enforced. The primary key is mainly associated with the foreign key of other tables, as well as the modification and deletion of this record.

1. Each table in the database can only have one primary key, not multiple primary keys.

2. The so-called multiple primary keys in a table are called federated primary keys.

Note: Union primary key: use multiple fields together as the primary key of a table.

3. The function of the primary key is to ensure the uniqueness and integrity of the data, and the retrieval speed can be increased through the primary key search table.

Let's talk about how to create a federated primary key:

1. Select multiple columns at the same time in GUI, and click set as primary key.

2. The sql statement sets multiple columns as primary keys:

One is to write it out when the table is created, with the following statement:

Create Table table name (field name 1 Int Not Null, field name 2 nvarchar (13) Not Null Primary Key (field name 1, field name 2), field name 3. Field name N. )

The other is to change the table after it is created, with the following statement:

ALTER TABLE table name WITH NOCHECK ADD CONSTRAINT [PK_ table name] PRIMARY KEY NONCLUSTERED ([field name 1], [field name 2]) above are all the contents of the article "how many primary keys are there in a single data table in the database". Thank you for reading! Hope to share the content to help you, more related knowledge, welcome to follow the industry information channel!