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one, key and primary key differenceCREATE TABLE Wh_logrecord (logrecord_id Int (one) not NULL auto_increment,User_name varchar (+) default NULL,Operation_time datetime default NULL,Logrecord_operation varchar (+) default NULL,PRIMARY KEY (logrecord_id),
--PRIMARY keyCREATE TABLE EMP (ID number constraint ID_PR primary key, name1 varchar (8));CREATE TABLE EMP9 (ID number, name1 varchar (8), constraint ABA_PR primary key (ID,NAME1));--FOREIGN keyCREATE TABLE EMP1 (ID number references emp (ID), name varchar (8));--composite F
MySQL in the index is very important knowledge points, compared to other knowledge points, the index is more difficult to grasp, and MySQL in the index of a lot of types, such as primary key, unique key and index, etc., this article to introduce you to the MySQL key, primary
Tags: des io ar using for SP strong data onone, key and primary key differenceCREATE TABLE Wh_logrecord (logrecord_id Int (one) not NULL auto_increment,User_name varchar (+) default NULL,Operation_time datetime default NULL,Logrecord_operation varchar (+) default NULL,PRIMARY KEY
one, key and primary key differenceCREATE TABLE Wh_logrecord (logrecord_id Int (one) not NULL auto_increment,User_name varchar (+) default NULL,Operation_time datetime default NULL,Logrecord_operation varchar (+) default NULL,PRIMARY KEY (logrecord_id),
Super key: An attribute set that uniquely identifies a tuple in a relationship is called a hyper-key of a relational patternCandidate key (candidate Key): A super-key that does not contain extra attributes is called a candidate keyPrimary
one, key and primary key differenceint (one) not NULL auto_increment, user_name varchar (defaultDefault NULL, logrecord_operation varchar (defaultAnalytical:KEY Wh_logrecord_user_name (USER_NAME)The User_name field in this table establishes a foreign key with the Wh_logrecord_user_name table user_name fieldOutside the
SQLServer sets two primary keys, and sqlserver sets the primary keyZookeeper First, a table cannot have two primary keys. However, two fields can be combined into a primary key, which is why two fields in the table sometimes have a prima
Super key: the attribute set that uniquely identifies a tuples in a link is called the super key of the link mode.Candidate Key: A super key without redundant attributes is called a candidate key.Primary Key (primary
Super key: the attribute set that uniquely identifies a tuples in a link is called the super key of the link mode.Candidate Key: A super key without redundant attributes is called a candidate key.Primary Key (primary
Primary key conflict-a table can have two primary keys. A new primary key statement can have two primary keys in the table: primary key for
Several primary key generation policies of Hibernate and several primary keys of hibernate Primary Key type:Business primary key (natural key
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 //
This article is referenced from:http://blog.csdn.net/bingqingsuimeng/article/details/51595560First, what is the primary key, foreign key:There are several attributes in a record in a relational database, which can be a primary key if one of the attribute groups (note is a group) uniquely identifies a record.Like whatSt
Label:First, what is the primary key, foreign key: There are several attributes in a record in a relational database, which can be a primary key if one of the attribute groups (note is a group) uniquely identifies a record: Student Table (School number, name, gender, Class)
First, what is primary key, foreign key:A record in a relational database has several properties, and if one of the attribute groups (note the group) uniquely identifies a record, the attribute group can be a primary key such as: Student form (school number, name, gender, Class) Each student's number is unique, and t
Set MySQL data table primary key: Use the "PRIMARY key" keyword to create a primary key data column. The primary key column is set to not al
Primary keys and foreign keys are binders that organize multiple tables into an effective relational database. The design of primary keys and foreign keys has a decisive impact on the performance and availability of the physical database.The database schema must be converted from a theoretical logical design to an actual physical design. The structure of the primary
Label:The role of the primary and foreign keys of sql: Foreign key value rule: A null value or a reference primary key value. (1) When a non-null value is inserted, it cannot be inserted if the value is not in the primary key tabl
1. Definition 1.1 What are primary keys and foreign keys 1.2 The role of primary and foreign keys 1.3 Differences between primary key, foreign key, and index 2. Primary k
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