sql create table primary key autoincrement

, we have seen that the existing structure has many drawbacks, mainly because of the complexity of the program, reduced efficiency, and unfavorable paging. To solve the preceding problem, this article proposes that when there is a master-slave relationship between the database tables in the background of the application system, a non-business field is added to the database table as the primary

illustrate how to use inner joins and nested queries to implement multi-table queries. In fact, all databases are the same, and SQL statements are generic.I. BASIC OBJECTIVESIt is known that in the test database, the school database can be self-contained, the following table exists:(1) The student table I_student, whi

Label:Iv. SQL PRIMARY KEY constraint PRIMARY KEY constraint uniquely identifies each record in a database table The primary key must contain

--alter table Historydata drop constraint Pk_historydataALTER TABLE HISTORYDATA ADD constraint Pk_historydata primary key (Collectiontime,code)Change primary keyDelete from Historydata where collectiontime between ' 2014-09-01 00:00:00 ' and ' 2014-11-01 00:00:00 ' and ID no

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

Tags: database mysql database--1. Working with databasesUse Ren;--2. Create a student tableCREATE TABLE Student(Sid INT UNSIGNED PRIMARY KEY auto_increment,--UNSIGNED (unsigned) auto_increment (self-increment)Sname VARCHAR (10),--only 10 characters can be savedSaddress VARCHAR (15)-only 15 characters are saved) Engine=

A relational table is actually a collection of a class of entities with common attributes. As defined by the collection, the elements in the collection cannot be duplicated. Similarly, there should be no duplicate records in the relational table. For example, in a student's table, it is not necessary or appropriate to have two records of the same student. In the

Summary When deleting data in a table with a parent-child relationship, we all know that you must delete the child table before deleting the data in the parent table. Yesterday we used to delete the child table first, then delete the parent table, delete the use of t

sets are called sub-queries. There are two types of sub-queries: One is to return only a single-valued subquery, at which point it can be used where a single value can be used, when a subquery can be considered a function that has a return value; Another is a subquery that returns a column of values, at which point the subquery can be thought of as a data table that is temporarily present in memory. Create