how to optimize sql query with multiple joins

Tags: tar create done Project class User A mat statusReference: https://bbs.csdn.net/topics/330032307There is a dictionary table in the database, which contains the ID field and the corresponding name fields.In another record table, there is a corresponding ID for the dictionary table above, and there are multiple fields that contain the ID field. It needs to be identified and used by name.SELECTa.ID as 'numbering',' Story' as 'type', A.title as 'tit

) String after conversion: Cursor is inefficient in SQL and is not recommended when the amount of data is large (>1 million) can severely affect performance. 2. Direct assignment in SQL query, this way the code is relatively simple. Code

select [Value] = Stuff ((select ', ' +modmb003 from MODMB detail where modmb=18 for XML Path (')), 1, 1, ')The role of stuff is to delete characters of a specified length and insert another set of characters at the specified starting pointSyntax:STUFF (character_expression, start, length, character_expression)Columns: SELECT STUFF (' abcdef ', 2, 3, ' IJKLMN ')The result is: AIJKLMNEFSQL query, multiple row

Label:Sample table TB data is as follows ID value—————1 AA1 BB2 AAA2 BBB2 CCC First Kind SELECTID,[Val]=(SELECT [value] +',' fromTb asbWHEREb.ID=a.id forXML PATH ("') ) fromTb asA The first display of results 1 AA,BB,1 AA,BB,2 AAA,BBB,CCC,2 AAA,BBB,CCC,2 AAA,BBB,CCC, The second Kind SELECTID,[Val]=(SELECT [value] +',' fromTb asbWHEREb.ID=a.id forXML PATH ("') ) fromTb asaGROUP byId The second kind of display 1 AA,BB,2 AAA,BBB,CCC, Third (rep

A WHERE rownumber > page Size * (page-1 Description, Page size: Number of rows per page; pages: pages. When using, replace "page size" and "page size * (number of pages-1)" with numbers. Other scenarios: If you don't have a primary key, you can use a temporary table, or you can do it with scenario three, but the efficiency will be low. When tuning is recommended, the query efficiency increases with the prima

number Employee Name Single SQL Public Dept getempbydeptno (int deptNo);}Writing test ClassesQuery department and employee single SQL@Testpublic void Onetomany () { Sqlsession sqlsession = Mybatisutil.getsession (); Ideptdao mapper = Sqlsession.getmapper (Ideptdao.class); Dept Dept = Mapper.getempbydeptno (1); SYSTEM.OUT.PRINTLN ("Department name" +dept.getdeptname ()); For (Emp emp:

Tags: from solution oca Condition query class where SEL and. comReprint Please specify source: http://www.cnblogs.com/dachen408/p/7457312.htmlIn the process of programming, often involves the query, and there are many conditions, and conditions can be empty, if judged individually, there will be many cases, the solution:Qsqlquery query (m_db); QString province =

Tags: static multiple queries convert nbsp pop rom write mysql 1. According to the need to query the MySQL statement, return three required parameters, not a data set 2. Write functions such as the following: public static void Getparas (string condition 1, out string return value 1, out string return value 2, out string return value 3){The return value is 1= string. Empty;The return value is 2= string. Emp

Author: IamlasongRequirements: Table content needs to be changed, changes in temporal table content, use of SQL official statement to update the table in several areas.Suppose that you update a field directly with the field name = subquery, multiple fields are updated, and the fields are written in parentheses, such as the following:Update TB_JG TSet t.jgfl = ' SD ',(T.zj_code, T.ZJ_MC) = (select A.zj_code,

SQL Server database paging query has been a short board of SQL Server, idle, come up with several methods, assuming that there are table article, Field ID, year ... (other omitted), Data 53,210 (customer real data, quantity is not large), paging query each page 30, query pag

Tags: Sql--创建测试表use FlygoIF OBJECT_ID(‘test‘) IS NOT NULL DROP TABLE testCREATE TABLE test( Id int IDENTITY(1,1) NOT NULL, Name varchar(50) NULL, Judge char(1) NULL, Mail varchar(50) NULL)GO--插入测试数据INSERT INTO test ( Name ,Judge ,Mail) SELECT ‘张三‘,‘Y‘,‘[emailprotected]‘ UNION ALL SELECT ‘李四‘,‘Y‘,‘[emailprotected]‘ UNION ALL SELECT ‘王五‘,‘N‘,‘[emailprotected]‘ GOSELECT * FROM test--查询多行合并DECLARE @Maliaddress varchar(8000)set @Maliaddress = ‘‘‘‘ + STUFF(

Whether you use int or varchar, multiple-selection queries for status are difficult to handle. For example, under normal thinking, the enum for Customerstatus is set as follows: Copy Code code as follows: [Serializable] public enum Customerstatus { New = 0, Active = 1, Overdue = 2, Suspended = 3, Closing = 4, Closed = 5 } The status value is stored as int in the database. What if I want to search the page for

Set ANSI_NULLS on go SET quoted_identifier in go -============================================= CREATE FUNCTION CSJ_CSJ (@id as int) RETURNS @temp Table --here returns a table of its own creation, where the fields are set according to their needs ( [id] int, [ZD] varchar (m), [XL] varchar ( As BEGIN insert INTO @temp select ID,ZD,XL from Deb- -Inserts the SQL statement from the