In ACCESS, the primary key refers to a column or a combination of multiple columns. Its value can uniquely identify each row in the table. It can enforce the entity integrity of the table. The primary key uniquely identifies a record. For fields, the basic standards are the three major database paradigms.
In ACCESS, the primary key refers to a column or a combination of multiple columns. Its value can uniquely identify each row in the table, and it can be used to enforce Entity integrity of the table.
The primary key is a field that uniquely identifies a record. The basic standards are the three major database paradigms:
1. The database table must have a field that uniquely identifies a record (also known as the existence of the primary key ).
2. All fields in the table must have a relationship with the primary key (also known as primary key dependency).
3. All fields in the table are only related to the primary key (also known as the unique correlation of the primary key).
A lot of data may be repeated, but the primary key cannot be repeated, so you have a legal basis to follow when you want to delete, modify, and query the database. Finding its primary key is the most accurate. If you find other fields, Multiple data may be listed repeatedly.
Extended information:
The primary key is mainly used for foreign key associations in other tables, as well as modification and deletion of this record.
A primary key can be created by defining a PRIMARY KEY constraint when creating or altering a table. A table can only have one PRIMARY KEY constraint, and the columns in the PRIMARY KEY constraint cannot accept null values. Since PRIMARY KEY constraints ensure unique data, they are often used to define identity columns.
Function:
1. Ensure the integrity of the entity;
2. Speed up the operation of the database;
3. When adding a new record to the table, the DBMS will automatically check the primary key value of the new record and will not allow the value to be repeated with the primary key value of other records;
4. DBMS automatically displays the table in the order of the primary key value. records in. If no primary key is defined, the records in the table are displayed in the order in which they were entered.
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