select count distinct

You can combine sp_msforeachdb to iterate through all the user databases to see the size of all the tables, note that its parameters @sql not exceed nvarchar (2000), where the code is not posted.You can also run periodically and save the results to

When using MySQL, there are times when you need to query for records that are not duplicated in a field, although MySQL provides a distinct keyword to filter out excess duplicates, but it often only uses it to return the number of records that are

First of all, some uses of MySQL's distinct keywords: 1. This can be used when count does not duplicate records, such as SELECT COUNT (DISTINCT ID) from tablename , or how many records with different IDs in the Talbebname table are counted. 2, you

The so-called index is a specific MySQL field for some specific algorithm sorting, such as the two-fork tree algorithm and hashing algorithm, the hash algorithm is established by establishing the eigenvalues, and then based on the characteristics of

1. Cardinality simply, the number of unique values of your indexed columns, if the composite index is the only number of combinations. 2. This value will be used as a basis for the MySQL optimizer to determine the statement execution plan. If

@Select ("select * from Wc_homework WHERE organization_id=#{classid} ORDER by Createtime DESC LIMIT #{start},#{count}") @Results ({ @Result (column = "course_id", property = "course_id"), @Result (column = "homework_id", property =

Recycle Bin: Show RecycleBin (command line statement) empty Recycle Bin: Purge recyclebin Recycle Bin restore deleted table: Flashback table table_name to before Dorp get system time: Sysdate Average: Avg Condition is true: where 1=1 condition is

some summarization on the optimization of hive performance Note that this article 90% from this article: Hive performance optimization, very grateful to the author of the careful collation, some of which I have done supplements and additions, if

V. User Login (login.php) At the beginning, we said that the entrance of the game is index.php file, we have already installed, the nature turns to the login process, starts to look. As usual, we will not go into the details of the code we have

In a MySQL query, duplicate values may be included. This is not a problem, but sometimes you may want to list only the different values (distinct). Keyword DISTINCT is used to return only a different value, that is, to go heavy. The usage is also

first, start and exit 1, into MySQL: Start the MySQL Command line Client (MySQL's DOS interface), directly enter the installation of the password can be. The prompt at this point is:mysql> 2, Exit Mysql:quit or exit Second, the library operation1.

1, Hive belongs to the Java system, the data encoding is Unicode, so the GB18030 from the production library is extremely encoded set of data, load to hive is likely to appear garbled. Fortunately there is a mapreduce, we can write a data cleaning

Good Article ~ ~ The work is very commonly used.Record learning.AC Group 127591054Original post address: http://www.3lian.com/edu/2013/11-29/111321.html after a large number of deletions to the table, there may be a lot of free space can be recycled,

Introduction to Grouping functions A grouping function acts on a set of data and returns a value for a set of data. The common grouping functions are: Function name Function description Count Returns the number of

Http://jt.photos.17173.com/photopic/find_result.asp Microsoft OLE DB Provider for ODBC Drivers error ' 80004005 ' [Microsoft] [ODBC SQL Server Driver] [DBNETLIB] SQL Server does not exist or access is denied /photopic/find_result.asp, line 34 After

server| Design | performance 1 logical database and table design The logical design of database, including the relationship between table and tables, is the core of optimizing the performance of relational database. A good logical database design

Server Topic 1Problem Description:Establish 3 tables for the management of job training information:S (S#,SN,SD,SA) S#,sn,sd,sa on behalf of the school number, student name, affiliation unit, student ageC (C#,CN) C#,CN represents the course number,

This function library is almost exactly the same as the SQL Server database function library, which is actually the first occurrence of this function before the SQL Server database function library appears. Sybase and MS SQL Server 6.x are almost

2005-3-3 learning Hibernate in learning hibernate, I found that for database sub fields in SQL server2000, the configuration file was implemented using the following methods: Class = "Identity"/> here is mainly: identity: Represents a

select| problem Hi,everyone: Today we continue to discuss select top N issues. 1. DB2 m 2 As mentioned in the previous discussion, M2 cannot be constructed because the DB2 subquery does not support an ORDER BY clause. In fact, DB2 provides a new