Sql Drop Primary Key

The complete collection of SQL statement operations deserves to be permanently stored the following statements are part of the MSSQL statement and are not available in Access. SQL classification: ddl-data Definition language (create,alter,drop,declare) dml-Data Manipulation Language (Select,delete,update,insert) dcl-Data Control Language (Grant,revoke, Commit,rollback first, briefly introduce the basic statement: 1, Description: Create number ...

Intermediary transaction http://www.aliyun.com/zixun/aggregation/6858.html ">seo diagnose Taobao guest cloud host technology Hall before writing a paging stored procedure, we first create a test table for the database. This test shows that there are 3 fields, called Order, which are or_id,orname,datesta; The following creates a table script: CREATE TABLE [dbo]. [Orders ...]

MySQL database sql statement commonly used optimization methods 1. Query optimization, should try to avoid full table scan, should first consider where and order by the columns involved in the establishment of the index. 2. Should be avoided in the where clause on the field null value judgment, otherwise it will cause the engine to abandon the use of indexes and full table scan, such as: select id from t where num is null You can set the default value of num 0, to ensure that Num column table does not null value ...

Introduction with the advent of the cloud computing era, various types of Internet applications are emerging, the relevant data model, distributed architecture, data storage and other database related technical indicators also put forward new requirements. Although the traditional relational database has occupied the unshakable position in the data storage, but because of its inherent limitation, has been unable to satisfy the cloud computing age to the data expansion, reads and writes the speed, the support capacity as well as the construction and the operation cost request. The era of cloud computing has put forward a new demand for database technology, which is mainly manifested in the following aspects. Mass data processing: to ...

With the rise of internet web2.0 websites, the relational database has become a very hot new field, the development of the non relational database products is very rapid. 　　But the traditional relational database in dealing with web2.0 website, especially the super large-scale and high concurrent SNS type web2.0 pure dynamic website already appeared to be powerless, has exposed many insurmountable problems, for example: 1, high configured--to the database higher concurrent reads and writes the demand WEB2.0 website to be based on user personalized information to generate real-time dynamic ...

Access analysis is an important SEO work, but statistics, analysis tools, after all, the function is for the public, many times SEO needs some specific data, is http://www.aliyun.com/zixun/aggregation/10341.html "> Statistical analysis software, procedures can not provide. 　　In this way, direct Web log analysis is the most appropriate, the log will record each visit, as long as their own will extract, combination, you can get the data you want. Just ask ...

Intermediary transaction http://www.aliyun.com/zixun/aggregation/6858.html ">seo diagnose Taobao guest stationmaster buy cloud host technology Hall Yesterday put one of my DZ forum from X2 upgrade to X2.5 appeared a problem, upgrade into a dead cycle, specific hints as follows: update.php?step=waitingdb&nextstep=prepare& sql[...

ALTER alter alter the name of the table structure of the name of the table ALTER TABLE ALTER TABLE ALTER TABLE statement is used to add, modify or delete columns in the existing table. sql alter table syntax To add a column to a table, use the following syntax: alter table table_name add column_name datatype To delete a column in a table, use the following syntax: alter table table _...

In the past few years, the innovative development of the open source world has elevated the productivity of Java™ developers to one level. Free tools, frameworks and solutions make up for once-scarce vacancies. The Apache CouchDB, which some people think is a WEB 2.0 database, is very promising. It's not difficult to master CouchDB, it's as simple as using a Web browser. This issue of Java open ...