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Cartesian productMulti-table query, multiple tables become a tableIntegrity constraint conditionsPrimary key identifies this property as the primary key for the table and can uniquely identify the corresponding tupleForeign key identifies this property as a foreign key of th
Label:Iv. SQL PRIMARY KEY constraint PRIMARY KEY constraint uniquely identifies each record in a database table The primary key must contain a unique value Primary
[Email protected]> CREATE TABLE emp_1 as SELECT * from EMP; --Schedule table created.[Email protected]> CREATE TABLE dept_1 as SELECT * from dept; --table created for main tables.[Email protected]> ALTER TABLE dept_1 add constraint pk_dept_1 primary key (DEPTNO);--primary table Add primary
First, create a tabular format:Create Tabletable name (Whether the Field field type can be empty, ...); Comment on columnTable/Field isAn example of a comment:Create TableCompany (com_idINTEGER not NULL, Com_nameVARCHAR2( +)NULL, Com_addressVARCHAR2( -)NULL); Second, create a primary key/FOREIGN Key1, create a PRIMARY
Label:1: What is a primary keyIn a table, the set of fields used to uniquely identify a record is called the primary key or primary key, or the primary key (or main code), which says "f
Label:Primary key a database primary key is a combination of one column or column in a table whose value uniquely identifies each row in the table. Such a column or columns is called the table's primary key, which enforces the entity integrity of the table. When you create o
Label:Primary key a database primary key is a combination of one column or column in a table whose value uniquely identifies each row in the table. Such a column or columns is called the table's primary key, which enforces the entity integrity of the table. When you create o
Primary keya database primary key is a combination of one column or column in a table whose value uniquely identifies each row in the table. Such a column or columns is called the table's primary key, which enforces the entity integrity of the table. When you create or chang
http://www.shangxueba.com/jingyan/122163.html primary key:1. PRIMARY KEY constraint: A table can have only one primary KEY constraint. The primary
Tags: SQL primary key foreign keyprimary KEY (Primary key) each of the data in the table is a unique value in the form. In other words, it is a unique way to identify each row of data in a table. The primary
Tags: integrity alt otto ack article ble sql ima back primary KEY (Primary key) each of the data in the table is a unique value in the form. In other words, it is a unique way to identify each row of data in a table. The primary key
Tags: mysqlFirst describe the cause of this problem, suppose there is a table, which holds the trade orders, each order has a unique ID, the last update time, and the data, the details are as follows:+-------+----------+------+-----+---------------------+-------+ |field|type |Null|Key|Default |extra| +-------+----------+------+-----+---------------------+-------+ |uid|int (11) |NO|PRI|0 | | |time|datetime|no|| 0000-00-0000:00:00|| |Data| Int (one) |YE
Tags: Lin paging query IDT multi-row GES Development Font Foundation designPrimary key a database primary key is a combination of one column or column in a table whose value uniquely identifies each row in the table. Such a column or columns is called the table's primary key
Tags: defining maintenance Records student Val Family index note STRPrimary key and foreign key of the database first, what is the primary key, foreign key: There are several attributes in a record in a relational database, which can be a
Both the Primary key and the unique key are unique constraints. But there's a big difference:1, Primary key 1 or more columns must be NOT NULL, if column is null, when the Primary key i
MySQL "on duplicate key update" SyntaxIf the on duplicate key update is specified at the end of the insert statement and the duplicate value appears in a unique index or primary key after the row is inserted, update is executed on the row with the duplicate value; if the unique value column is not duplicate, a new row
Database:Warehouse where data is stored, data is classified by tableFeatures: mass storage, fast searching, control of concurrency problems, security, data integrity (the data stored in the database is correct and true)database software: DBSM Database Management SystemCommon database software: MySQL MSSQL Server Oracle AccessSQL: Structured Query Language Structured Query Language features: Simple language, easy to learn and easy to use.SQL Server: is a large network-based database software. The
For example, the commodity table and the attribute table, because it is many-to-many relationship, so there is a commodity attribute intermediate table; CREATE TABLE IF not EXISTS dslxs_goods_attr( goods_idMediumint (8) unsigned not NULL COMMENT ' Product ID ', attr_idMediumint (8) unsigned not NULL COMMENT ' property id ', KEY goods_id( goods_id), KEY attr_id( attr_id) Engine=innodb DEFAULT Charset=utf8
This article mainly introduces in inserting the data to the table to encounter the key duplication avoids inserting the duplicate value the processing method, mainly relates to Ignore,on DUPLICATE key update,replace; then look at the three ways to deal with each. IGNORE Using ignore automatically ignores duplicate record rows when the inserted value encounters a prima
1. Add delete primary key and foreign key For example: -----Delete a PRIMARY KEY constraintDECLARE @NAME SYSNAMEDECLARE @TB_NAME SYSNAMESET @TB_NAME = ' Date 'SELECT TOP 1 @NAME =name from SYS. OBJECTS with (NOLOCK)WHERE type_desc = ' primary_key_constraint ' and parent_o
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