sql query optimization techniques

with exists instead of in is a good choice:Select num from a where num in (select num from B)Replace with the following statement:Select num from a where exists (select 1 from b where num=a.num) \14, not all indexes are valid for the query, SQL is based on the data in the table to query optimization, when the index co

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

considerations for improving query speed, but in many other cases, it is often necessary to repeatExperiment with different statements to get the best solution. The best way to do this, of course, is to look at the SQL language that implements the same function.Which run time is the least. However, the database assumes that the amount of data is very small, is less than the comparison. You can then use the

cursors are inefficient and should be considered for overwriting if the cursor is manipulating more than 10,000 rows of data.26. Before using a cursor-based method or temporal table method, you should first look for a set-based solution to solve the problem, and the set-based approach is generally more efficient.27. As with temporary tables, cursors are not unusable. Using Fast_forward cursors on small datasets is often preferable to other progressive processing methods, especially if you must

course where cname = " database base ") \g; The second way Desc Select B.sno,b.ssex,a.grade from (select Sno,ssex,sname from student) as B, (select Sno,grade from SC where CNO = (select Cno from course where cname= " database base c3>")) as a where A.sno = B. Sno \g; (3) Summary usually nested queries recommend using Join...on ... statement, which reduces the creation of temporary tables because Select clause creates a temporary table Although none of the above statements use Join...on ... st

Label:Use the following statement to find the most frequently executed SQLDB2 SELECT * FROM Sysibmadm. Snapdyn_sql ORDER BY Num_executions Desc,total_sys_cpu_time_ms desc FETCH first 205 rows only >>D:\NUM_EXECUTIONS.T XtThe file that opens the output appears as follows:Determine if there is a problem based on the number of executions. If you find that the number of executions is significantly higher, you should see if there is a problem in the program. In general, the basic data will be more th

SQL General optimization scheme:1. Using parameterized queries: Prevent SQL injection and precompile SQL commands for increased efficiency2. Remove unnecessary queries and search fields: In fact, in the actual application of the project, many of the query conditions are opti

Label: first, SQL statement optimization 1-1.mysql Slow Log 1). Slow log on mode and storage formatHow do I find the problematic SQL? Use MySQL slow logs to monitor efficiency issues with SQL Pre-preparation Mysql> Show variables like '%log_queri% '; +-------------------------------+-------+ | Variable_name

Tags: uniform having text get data BSP Execution plan calculations take advantage of specificFive optimization techniques 1. Query reuse refers to the use of the previous execution results as far as possible, in order to save the query calculation of the whole process of time and reduce resource consumption. At present

never be finished! Quick review of the best 10 tips * Use sufficient agents for the workload. * Do not allow DB2 to close and open files unnecessarily. * Long-term lock waits are not allowed. * Ensure the parallel I/O capability of the Tempspace table space of the database. * Conservative management of DB2 sort memory does not have to cover sorting problems with large SORTHEAP. * Analyze the table's access activity and determine the table that has a particularly hi

Apache Server Optimization ,PHP optimization , mysql optimization For program developers, the two most popular background databases are MySQL and SQL Server. The basic similarity between the two is the data storage and the query system. If you want to build a. NET

For helpDB2DBA avoids performance disasters and achieves high performance. I have summarized a fault diagnosis process for our customers, users, and DB2 experts. The following describes in detail the 10 most important performance improvement techniques for using DB2 UDB's e-commerce OLTP applications in Unix, Windows, and OS/2 environments, at the end of this article, we will make a summary.DB2 databaseOfOptimizationWork is an important part of DB2. T

Introduction: MySQL databaseThe optimization of MySQL database is a very important work link. The optimization of MySQL database is skillful. The following describes the top 10 optimization techniques of MySQL database, I hope this will help you. 1. Optimize Your MySQL query

,neibuyonghu,reader,title from Tgongwen where fariqi> ' 2004-1-1 ' and fariqi4. The date column will not slow down the query speed because there is a minute or seconds inputIn the following example, there are 1 million data, 500,000 data after January 1, 2004, but only two different dates, the date is accurate to the day, before the data 500,000, there are 5,000 different dates, the date is accurate to the second.Select Gid,fariqi,neibuyonghu,reader,t

Mysql uses indexes for query optimization and mysql index Query Optimization The purpose of indexing is to improve the query efficiency. It can be analogous to a dictionary. If you want to query the word "mysql", you must locate t

Database optimization tutorial (3) Slow query of records and database optimization tutorial Query1. Slow query foundIn the previous section, we made data preparation for slow queries. This section allows us to find slow queries and record them to files. 3. Slow query of reco

Database optimization tutorial (3) Slow query of records and database optimization tutorial Query1. Slow query foundIn the previous section, we made data preparation for slow queries. This section allows us to find slow queries and record them to files. 3. Slow query of reco

This paper summarizes the indexing usage of MySQL database optimization technology. Share to everyone for your reference, specific as follows: Here is a summary of the configuration techniques of MySQL database optimization technology to further analyze the techniques of index opt