Difference Between Null And Not Null In Sql

1.1: Increase the secondary data file from SQL SERVER 2005, the database does not default to generate NDF data files, generally have a main data file (MDF) is enough, but some large databases, because of information, and query frequently, so in order to improve the speed of query, You can store some of the records in a table or some of the tables in a different data file. Because the CPU and memory speed is much larger than the hard disk read and write speed, so you can put different data files on different physical hard drive, so that the execution of the query, ...

SQL used to manipulate the database is generally divided into two kinds, one is the query, which is what we call the SELECT statement, the other is to update the statement, also known as data manipulation statements. The implication is to modify the data. There are 3 statements in the standard SQL, which are INSERT, UPDATE, and DELETE. There is another REPLACE statement in MySQL, so this article uses MySQL as a background to discuss how to make updates in SQL. First, INSERT and REPLACE I ...

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 ...

Fourteen make PHP beginners a big headache Summary Today for everyone to give PHP beginners a headache big summary, the following 14 questions hope for PHP beginners to help. 1, the page can not be passed variables get, post, session Automatic global variables in the latest php version is turned off, so to get over the variables from the previous page to use $ _GET ['foo'], $ _ POST [ 'foo'], $ _ SESSION ['foo']. Of course it can be ...

Spark can read and write data directly to HDFS and also supports Spark on YARN. Spark runs in the same cluster as MapReduce, shares storage resources and calculations, borrows Hive from the data warehouse Shark implementation, and is almost completely compatible with Hive. Spark's core concepts 1, Resilient Distributed Dataset (RDD) flexible distribution data set RDD is ...

HBase is a distributed, column-oriented, open source database based on Google's article "Bigtable: A Distributed Storage System for Structured Data" by Fay Chang. Just as Bigtable takes advantage of the distributed data storage provided by Google's File System, HBase provides Bigtable-like capabilities over Hadoop. HBase Implements Bigtable Papers on Columns ...

Using hive, you can write complex MapReduce query logic efficiently and quickly. In some cases, however, the Hive Computing task can become very inefficient or even impossible to get results, because it is unfamiliar with data attributes or if the Hive optimization convention is not followed. A "good" hive program still needs to have a deep understanding of the hive operating mechanism. Some of the most familiar optimization conventions include the need to write large tables on the right side of the join, and try to use UDF instead of transfrom ... Like。 Here are 5 performance and logic ...