how to optimize sql query with multiple joins

accurate execution plan. Create a statistic for the condition by using the following statement Statistics businesstablefilterstatistics on businesstable (BUSINESSSTATUS1,BUSINESSSTATUS2) where BusinessStatus1= andBusinessStatus2=--withfullscan After the statistics are created, a statistic that you just created is added to the table. Now look at the execution plan for this query, and find that it goes through the index as expected While o

Q A location: http://space.cnblogs.com/q/20546/q A: I have asked more questions about the relationship: 5 [resolved issues] Browse: 52 times 00 Student table T1 Stu_id Stu_name 1 Zhang San 2 Li Si 3 Wang Wu Course list T2 Co_id Co_name 1 Java 2 C # 3 C 4 C ++ 5 Javascript Link Table T3 Stu_id Co_id 1 1 1 4 2 1

Recently, a development team complained that the mysqlcluster on our platform was not good and always reported mysql heartbeatError. after analyzing the logs they collected, they did not find any network problems between mysqlcluster nodes, however, I found a very interesting phenomenon. Recently, a development team in mysql's sl complained that the mysql cluster included in our platform was not good and always reported the "heartbeat Error" of mysql. I analyzed the logs they collected and found

between Multiple indexes to completely overwrite a query. If the covered index becomes very wide, you can consider the index connection.For this SQL statement (select UserName, Gender from dbo. UserInfo where UserName = 'usern600 'and Gender = 1), you can create a non-clustered index on Gender.In this example, the SQL

an index crossover between Multiple indexes to completely overwrite a query. If the covered index becomes very wide, you can consider the index connection.For this SQL statement (select UserName, Gender from dbo. UserInfo where UserName = 'usern600 'and Gender = 1), you can create a non-clustered index on Gender.In this example, the

is best to use INCLUDE in the following situations: 1. You do not want to increase the size of the index key, but you can still create a Covering Index; 2. It is intended to index a data type that cannot be indexed (except text, NTEXT, and image ); 3. the maximum number of keyword columns for an index has been exceeded. Method 3: Connect using Indexes An index connection uses an index crossover between Multiple indexes to completely overwrite a

SQL data query optimization select nbsp;. id, rkno,. packageno nbsp; as nbsp; packageno, cust_no, lotno, count (*) nbsp; as nbsp; count nbsp; from nbsp; 'rk _ record ' nbsp; as nbsp SQL data query optimization Select. id, rkno,. packageno as packageno, cust_no, lotno, count (*) as count from 'rk _ record 'as a

SQL data query optimization select nbsp;. id, rkno,. packageno nbsp; as nbsp; packageno, cust_no, lotno, count (*) nbsp; as nbsp; count nbsp; from nbsp; 'rk _ record ' nbsp; as nbsp; a nbsp; right nbsp; join nbsp;'s SQL data query optimization Select. id, rkno,. packageno as packageno, cust_no, lotno, count

efficiency of cross-month queries is not considered for the time being, because users are rarely used. However, you need to check two tables, one is the history table and the other is the back _ current month table. Because the name of the next table is unknown, a lot of dynamic query statements are used in the stored procedure to pass the table name. The two tables are separately queried, and then the records are merged using union. One is the sit

SQL Duplicate record query 1, look for redundant records in the table, duplicate records are based on a single field (Peopleid) to judge SELECT * from people where Peopleid to (select Peopleid from People GROUP by Peopleid have count (Peopleid) > 1) Case Two: SELECT * from TestTable where Numeber to (select number from people group by number has count (number) > 1) can detec

Recently and colleagues to deal with a small program, the data volume is not particularly large, a table of data records: 7000W records around, but from the change to execute a query, but found that the query is not fast, and the most obvious problem is cpu100%.SQL statements:Select from where LNG> and LNG and lat> and LatMax_lat;To find the problem, use the fol

(BUSINESSSTATUS1,BUSINESSSTATUS2)The following query is to query the so-called special dataSELECT * from businesstable where businessstatus1=3 and businessstatus2=10Find the execution plan as follows: The whole table scan, the IO cost is not small,In this case, obviously there is only one data, but to go full-table scan(There is not only one such coincidence in the actual business, but in the Tens table, t

Hibernate native SQL query Multiple table Association, SQL statement to pay attention to the problem@for ever 2009-9-4System environment:MySQL5.1Hibernate3.3The assumption is as follows:The entity classes Question and answer correspond to the data table Question and answer respectively.and the fields of table question

subqueries, multiple table queries, federated queriesThese three concepts are interpreted slightly differently in different versions of SQL, roughly as follows: Join connectionCan look at the relevant SQL information, or buy a book of SQL 1, such as: SELECT * from TAB1 where ID in (SELECT id form tab2 where ...)The

First, simple query:Basic Syntax: The code is as follows Copy Code SELECT * from Tb_name; Query all The code is as follows Copy Code SELECT field1,field2 from Tb_name; Projection The code is as follows Copy Code SELECT [DISTINCT] * from Tb_name WHERE qualification; ChooseDescription FROM clause: Relational table,

The original author seems to be called topcat. I understood it myself and wrote it back with my memory.If Select Name From StudentTable is used, the result is:NameZhang SanLi SiIf Select ROW_NUMBER () as rowindex, Name From StudentTable is used, the displayed result isROWINDEX Name1 Zhang San2 Li SiOf course, you do not need to add numbers to the query results, because the List itself has numbers when displaying data. But the advantage of this is that

Usage scenarios:For example, you need to query all student numbers with scores greater than 95, separated by commas into a string, from the Student score table.To prepare the test data:CREATE TABLE score (ID int,score int)INSERT into score values (1,90)INSERT into score values (2,96)INSERT into score values (3,99)It is now necessary to query the result string "2,,3" with a single statement.The

This tutorial for you to introduce the SQL of the multiple table query, let's look at the specific examples. Create a new two sheet: Table 1:student screenshot as follows: Table 2:course screenshot as follows: (This is just a table to demonstrate the connection of SQL statements, of course, in the actual develo

Create a new two sheet: Table 1:student screenshot as follows: Table 2:course screenshot as follows: (This is just a table to demonstrate the connection of SQL statements, of course, in the actual development we do not build tables, the actual development of the two tables will have their own different primary key.) ） One, outer connection Outer joins can be divided into: Left join, right connecti

SQL multiple table joint query two query instances First look at the common query Two table structures are differentSelect m.*, n.* from t1 m, t2 n where m.id = N.idand n.date = (select Max (date) from t2 where id = n.id) Select m.*, n.* from t1 m, t2 n where m.id = N.idA