Ví dụ về việc sử dụng The primary key trong Tiếng anh và bản dịch của chúng sang Tiếng việt
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Colloquial
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Computer
You miss the primary key.
The primary key must be unique and not null.
They call it the Primary Key.
The Primary key attribute contains unique values.
Should the primary key be called“id”?
For example, assume we have a usertable with a numeric ID(the primary key) and an email address.
In this table, the primary key consists of CUST_ID and ORDER_ID.
Any columns that link to anothertable should be named the same as the primary key of that table.
Update the primary key index to add a record for the new tuple.
Entity integrity dictates that the primary key value cannot be Null.
In other words, each field in a record shouldcontain information about the entity that is defined by the primary key.
Having NULL values for the primary key implies that we cannot identify some tuples.
Titles in the table, field PubID called Foreign Key, which means that this is the Primary Key of a table is(Foreign).
Entity Integrity Rule said that the Primary Key is indispensable, ie values can not be NULL.
If the Primary Key Row containing the records were deleted,the corresponding tableside nhiều(∞) was deleted by.
This is like an SQL database table where the primary key is pre-set by the system and is always time.
Instead of holding a pointer to the on-disk row location(like the ctid does in Postgres),InnoDB secondary index records hold a pointer to the primary key value.
For example, to drop the primary key constraint in the EMPLOYEES table, you can use the following command.
Access also makes sure that every record has a value in the primary key field, and that the value is always unique.
In the Relationships window, drag the primary key from the table on the"one" side of the relationship and drop it on the Foreign key field of the table on the"many" side of the relationship.
It's possible you mighthave a perfectly valid need to change the primary key for a shipper that has orders in the Orders table.
Consider the following definition of the table Orders,which defines a foreign key relationship referencing the primary key of the Customers table.
In the Combine Rows Based on Column dialog, select the column you want to remove duplicate from andclick Primary Key to make it as the primary key column. See screenshot.
Note: If you use the ALTER TABLE statement to add a primary key, the primary key column(s) must already have been declared to not contain NULL values(when the table was first created).
An association between two tables in which the primary key value of each record in the primary table corresponds to the value in the matching field or fields of one, and only one, record in the related table.
Cascade(chain effect): If the value is changed, the Primary Key Foreign Key corresponding to the numbers in the records of the table side nhiều(∞) is changed.