db2 query optimization

ManyProgramWhen developers use some front-end database development tools (such as PowerBuilder and Delphi) to develop database applications, they only pay attention to the gorgeous user interface and do not pay attention to the efficiency of query statements, as a result, the developed application system is inefficient and resources are wasted heavily. Therefore, it is very important to design efficient and reasonable

Analysis of Index Condition Pushdown (under the ICP Index Condition) and Multi-Range Read (MRR Index Multi-Range lookup) query optimization in MySQL, Source: http://www.cnblogs.com/wy123/p/7374078.html(The Source retained is not the right of original works. My work is far from reaching this level, just to link to the original article, because some possible errors will be corrected or supplemented later, wi

MVCC schema. The cost estimate in the execution plan is not equal to the actual cost of execution. So even if the statistical information is accurate, the optimizer's execution plan may not be a crime-superior. For example, sometimes an execution plan needs to read more pages, but his cost is even smaller. Because if these pages are sequential read or the pages are already in memory, the cost of access will be minimal. MySQL level and only know those pages in memory, those on disk, so the

Optimizing UnionUnion has an interesting optimization that exists except ss a few different databases. it's obvious when you think about how it works. union gives you the rows from two tables that don't exist in the other. so implicitly, you are removing duplicates. to do thisThe MySQL database must return distinct rows, and thus must sort the data. sorting, as we know is expensive, especially for large tables. Union all can very well be a big speedup

Tags: MySQL database If a large table contains millions, tens of millions, or even hundreds of millions of data records, the query results should be queried in real time within 10 seconds. What should I do? How to optimize it? In my current project, there is a table with more than 10 million rows of data and more than 3 GB of data. Now we need to perform query statistics on the data in the table. Previo

Label:SQL server2005 optimization Query Speed 50 Summary of methodsSQL server2005 Optimization Query speed 51 method Query Slow reason many, common following several, we can refer to below.I/O throughput is small, creating a bottleneck effect.A computed column is not created

The basic task of a database is to store and manage data, and the only database feature that an end-user can see is its performance: how quickly the database processes the results of a given query, and returns the results to the tools and applications used by the user. From the application examples of most systems, query operations occupy the largest proportion in various database operations, access to news

The following articles mainly describe five useful methods for MySQL query optimization. Anyone familiar with SQL statements knows that if you want to operate a task, SQL statements can be written in many ways, but the query performance varies with different writing methods. This article lists five MySQL query

performance and compromises the user experience. First, let's sort out the SQL statement. taking the first one as an example, we have joined multiple tables to query, and whether the multiple tables are necessary and there is a possibility of logical optimization. The primary table we query is the resignation information table, which is associated with three tab

This article mainly introduces the MySQL index and slow query optimization tutorials shared by the technical team of Meituan network, and analyzes some optimization solutions based on the actual disk IO situation, which is very recommended! If you need it, you can refer to MySQL, which has become the first choice for most Internet companies thanks to its outstand

Tag: Style color IO using strong SP data on problemIn recent times, has been exploring the SQL Server query performance issues, of course, also aimless search for a lot of information, but also from the online great God's articles learned a lot, here, to the great God salute. It is by the great God selfless dedication of the influence of the spirit, so, the younger brother also in return, share about the set STATISTICS io and set STATISTICS time these

Many programmers think that query optimization is the task of the DBMS (Database Tutorial management System), which is not related to the SQL statements written by programmers, which is wrong. A good query plan can often improve the performance of the program by dozens of times times. A query plan is a collection of SQ