complicated sql queries

Tags: MySQL sql slow log optimizerPrevious article: MySQL5.6 How to optimize SQL statements for slow queries--Slow log introductionIn the actual log analysis, usually slow log number of logs, while the same query is logged a lot of bars, here you need to find the most problematic from the slow log query, the most need to optimize the log. In this regard, there ar

This article is guided by: The trigger causes deadlock, the job is many and frequent, the use of the middle table, the large number of cursors, the design of the index is unreasonable, the transaction operation is frequent, the SQL statement design is unreasonable, will cause the query inefficient, affect the performance of the server. We can use SQL Server's own profiling Trace tool

generic list. Use tolist VaRQ =FromEInDB. EmployeesWhereE. hiredate> =NewDatetime(1994, 1, 1)SelectE;ListEmployee> Qlist = Q. tolist (); 4. todictionary: converts a sequence into a dictionary. You can use the enumerable. todictionary VaRQ =FromPInDB. ProductsWhereP. unitsinstock SelectP;DictionaryInt,Product> Qdictionary =Q. todictionary (P => P. productid );Foreach(IntKeyInQdictionary. Keys){Console. Writeline (key );} Statement Description: In this example, the direct key expression

How to dynamically number rows and add row numbers in SQL is a classic problem in database queries. How to dynamically number rows and add row numbers in SQL is a classic problem in database queries. (1) display and sort row numbers 1. SQL Server row number A.

SQL Server queries table indexes and SQL Server Indexes SELECT index name = a. name , Table name = c. name , Index field name = d. name , Index field location = d. colid FROM sysindexes a JOIN sysindexkeys B ON. id = B. id AND. indid = B. indid JOIN sysobjects c ON B. id = c. id JOIN syscolumns d ON B. id = d. id AND B. colid = d. colid WHERE. indid not in (0,255

(1) display and sort row numbers1. SQL Server row number A. SQL 2000 uses identity (int,) and temporary tables to display row numbers.SELECTIdentity (int, 1, 1) as rownum,[DataID]INTO #1FROM DATASOrder by DataID;SELECT * FROM #1B. SQL 2005 provides a very useful function row_number (),Can be directly used to display the row number, of course, you can also use

(1) display and sort row numbers 1. SQL Server row number A. SQL 2000 uses identity (int,) and temporary tables to display row numbers.SELECTIdentity (int, 1, 1) as rownum,[DataID]INTO #1FROM DATASOrder by DataID;SELECT * FROM #1B. SQL 2005 provides a very useful function row_number (),Can be directly used to display the row number, of course, you can also use

Implementation methods of Database SQL recursive queries in different databases, SQL Recursion This article describes how to implement SQL recursive queries in different databases. For more information, see the following. For example, the table structure data is as follows:

amount of data, it is recommended to use a linked server --Create a linked serverexec sp_addlinkedserver ' srv_lnk ', ' ', ' SQLOLEDB ', ' Remote server name or IP address 'exec sp_addlinkedsrvlogin ' Srv_lnk ', ' false ', NULL, ' username ', ' password ' --query ExampleSELECT * from Srv_lnk. Database name. dbo. Table name--import ExampleSELECT * into table from Srv_lnk. Database name. dbo. Table name--delete the linked server after processing is completeexec sp_dropserver ' srv_lnk ', ' droplo

It's cool to manipulate the database on play with functional framework slick. But sometimes, because of some special scenarios, you have to use native SQL. Fortunately slick support this notation, you can look at slick official documents, slick Plain SQL queriesHttp://slick.lightbend.com/doc/3.1.1/sql-to-slick.html#slick-plain-

One SQL statement queries multiple databases and multiple SQL statements Requirement: An SQL statement is used to query the associated results from multiple databases and output them to the client. Investigation: The spring framework can configure multiple data sources. SQL