Sql Null Comparison

&http://www.aliyun.com/zixun/aggregation/37954.html ">nbsp;     SQL connections can be divided into internal, external, and cross joins. Database data: Book table ...

I now need to remove the latest content from each category as follows: select * from test group by category_id order by `date` The result is as follows. This is not the data I want, because msyql has the order of execution is the order of reference write: select ... from ... where .... group by ... having ... order by .. Execution order: ...

1, use the index to traverse the table faster. The index created by default is a non-clustered index, but sometimes it is not optimal. Under non-clustered indexes, the data is physically stored on the data page. Reasonable index design should be based on the analysis and prediction of various inquiries. In general: a. There are a large number of duplicate values, and often range query (>, <,> =, <=) and order by, group by occurred columns, consider the establishment of cluster index; Column, and each column contains duplicate values ​​can be ...

1, use the index to traverse the table faster. The index created by default is a non-clustered index, but sometimes it is not optimal. Under non-clustered indexes, the data is physically stored on the data page. Reasonable index design should be based on the analysis and prediction of various inquiries. In general: a. A large number of duplicate values, and often range query (>, <,> =, <=) and order by, group by occurred column, consider the establishment of cluster index; b. Column, ...

In the previous article, we learned more about SDS's work and operation process through SSDs Explorer. 　　In this article, we will explain in detail how to use the programmer's method to manipulate SDS. SDS provides SOAP and rest two kinds of interfaces, here we use rest+c# method to explain. 　　Soap is the same as it is, please check MSDN with interested students. Less gossip, let's take the example of creating authority, giving the "universal framework" of the rest Operation SDS: public s ...

Lucene.Net is an open source project for Full-text indexing that is currently widely used in. NET environments and is used for full-text indexing in project development. A few small problems in the development process are searching for multiple fields and multiple indexed directories. 1, a multiple-field search is to have more than one field of the content of the comparison search, similar concepts in SQL is select * from Table where a like '%query% ' or b '%query% '. Luce ...

After completing one of the biggest projects of the year, the focus is shifting from PM's role to storage-related work, so it took some time outside of the work to focus on NoSQL related information (mainly from blog.nosqlfan.com) NoSQL related [translate] nosql ecosystem Http://blog.nosqlfan.com/html/2171.html//This is the best and most complete document I have seen NoSQL speak about nos ...

It is well known that query optimization is an unavoidable topic in any database. For database engineers, optimization is the most challenging job. MySQL Open source database is no exception. In fact, the author believes that the database optimization is not as much as we imagine the suffering. 　　Under normal circumstances, you can start from the following four details to do a good job in the MySQL database query optimization. First, use the Explain keyword to evaluate the flaw in the query statement as shown in the following figure, now the author in the database to execute a simple select ...