foreign key field access

This article mainly introduces the difference and connection between the primary key and the foreign key in MySQL. it is the basic knowledge in MySQL beginners. if you need it, you can refer to the relationship between the primary key and the foreign

MySQL creates a primary key, a foreign key, and a composite primary key. For more information, see. MySQL creates a primary key, a foreign key, and a composite primary

database level. They are the database implementation method of "Reference integrity" as described in the basic database theory. Foreign key attributes can certainly be removed. If you don't want to use these constraints, it will certainly not affect programming, however, the "reference integrity" check is not performed for the input data. For example, there are two tables A (A, B): A is the primary

Primary key: There are several attributes in the record, and if one of the attribute groups (note is a group) can uniquely identify a record, the attribute group can become a primary key;PRIMARY key //primary keyYour foreign key is the primary

in the table does not have a foreign key associated with it).index is used to quickly look for records that have a specific value. Mainly for the convenience of retrieval, is to speed up access, according to certain rules created, generally play the role of sorting. The so-called Uniqueness Index , which is basically the same as the previous "normal index", has

ORACLE Database Table creation, auto-incrementing primary key, foreign key syntax explanation, oracle primary key1. Create a table structure: Drop table base_list; Create table base_list ( "DATA_LIST_ID" number not null, "BASE_DATA_ID" number not null, "BASE_DATA_LIST" VARCHAR2 (100 BYTE) not null, "FLAG" number default 0 NOT NULL ) LOGGING NOCOMPRESS NOCACHESequ

curriculum.Primary keys and foreign keys are defined primarily to maintain the integrity of the relational database.Summarize1. A primary key is a unique identifier that can determine a record. For example, a record includes an identity plus, last nameName, age.The ID number is the only one who can determine who you are. Others may have duplicates, so the ID numberis the primary

contains the item ID field, the item ID field also exists in the item table of document 2. If the foreign key is not pulled, after the item with the item ID 3 is used in document 1 and 2, the product name cannot be found when the document is 1 or 2. When there are few tables, some people think that data integrity and

1. Create PRIMARY KEY syntax ALTER TABLE table_name ADD CONSTRAINT pk_name PRIMARY KEY (column name); 2. Create FOREIGN KEY syntax ALTER Table news_info[child table name] ADD CONSTRAINT fk_news_info_news_type[constraint name] FOREIGN

A basic table new two tables: Table1 and table2 Table 1 (id,uid,name), the UID is a set of foreign keys, the foreign key does not have to set the automatic self increase and unsigned place do not draw √. ID as the primary key, set to self increase. Table2 (Uid,name), the UID is set to self increase. Note (the Table1