set null

1. Create a column ALTER TABLE tablename add COLNAME type NOT null default ' 0′; Cases: ALTER TABLE Mmanapp_mmanmedia add appid_id integer NOT null default 372; 2. Delete Column ALTER TABLE tablename drop

In a project, when we build a data form, two representations are associated, and the data in one table is completely dependent on the data of another table, FOREIGN KEY constraint syntax [CONSTRAINT [Symbol]] FOREIGN KEY[Index_name]

outside of MySQL key constraintThere are two common engine types for MySQL: MyISAM and InnoDB. Currently only the InnoDB engine type supports foreign key constraints. The syntax for INNODB FOREIGN KEY constraint definitions is as follows:[CONSTRAINT

Recently just contacted MySQL, in the establishment of the expression encountered some problems, always prompt error code: The Can ' t create table ..., so I went to the internet to search for a bit of the following points to note:[CONSTRAINT

Transferred from: http://blog.csdn.net/cnjsnt_s/article/details/5548280For specific use, refer to: http://blog.csdn.net/codeforme/article/details/5539454There are two common engine types for MySQL: MyISAM and InnoDB. Currently only the InnoDB engine

transferred from: http://blog.csdn.net/codeforme/article/details/5539454foreign KEY constraints The meaning of the child table:Insert/update is not allowed on a child table if a candidate key is not found in the parent tableWhat foreign KEY

MySQL foreign key set up detailed(1) Use of foreign keys: The role of the foreign key, there are two main:         One is to let the database itself through the foreign key to ensure the integrity and consistency of the data         One is

Creating and updating a data table is an operation-level object in a relational database. In relational databases, data records are stored through data tables. Primary keys, foreign keys, constraints, and indexes are often used in data tables. This

MySQL storage engine note storage engine overview plug-in storage engine is one of the important features of MySQL database, users can choose how to store and index data, whether to use things, and other features such as www.2cto.com based on

Mysql -- foreign key (froeign key), mysql -- froeign If a field of an object points to the primary key of another object, it is called a foreign key.The object to be pointed to is called a primary object (a primary table) or a parent object (a

MySql storage engine Introduction MySQL5.5 and later are used by defaultInnoDBThe storage engine. InnoDB and BDB provide transaction security tables. Other storage engines are non-transaction security tables.To modify the default engine, you can

I. Commonly Used MySQL command line commands1. Start the MySQL service. Net start MySQL Stop MySQL service. net stop MySQL 2. netstat-Na | findstr 3306: Check the listening port. findstr is used to check whether the following port exists. 3. log on

Foreign key: Data consistency and integrity are maintained to control data stored in the foreign key table. Associate two tables. The foreign key can only reference the values of columns in the External table!For example:A and BTable A contains the

1. Start the MySQL service. Net start MySQL Stop MySQL service. net stop MySQL 2. netstat-Na | findstr 3306: Check the listening port. findstr is used to check whether the following port exists. 3. log on to the MySQL console using the MySQL commend

Mysql cascade operations (instances) and mysql-level operation instances MySQL only supports the InnoDB Storage engine for Foreign keys. When creating foreign keys, the parent table must have corresponding indexes, when a sub-Table creates a

The primary key task is to help MySQL determine the location of a specific data record in the data table as quickly as possible. The primary key must meet the following two conditions: 1. The primary key must be unique. The primary key fields in

Mysqlinnodb foreign key Mysql foreign key BitsCN.com Mysql innodb foreign key Meanings of foreign key constraints on subtables: If no candidate key is found in the parent table, insert/update is not allowed in the child table. Description

4. create and update a data table bitsCN.com A data table is an operation-level object in a relational database. In relational databases, data records are stored through data tables.Primary keys, foreign keys, constraints, and indexes are often used

Take a look at the following code: # Foreach ($ ID in [1 .. 50]) # Set ($User = $ user. Get ($ id )) $ ID: $ {user. name} # End In the above Code, assume that only one user with the ID of 1 exists, but it will show that 50

MySQL storage engine sorting and MySQL storage engine sorting01.MyISAMDefault storage engine before MySQL 5.0. MyISAM does not support transactions or foreign keys. Its advantage is that the access speed is fast, you can use this engine to create