db2 query optimization

MySQL optimization-performance analysis and query optimizationoptimization should be carried out throughout the product development cycle, such as when writing complex SQL to view the execution plan, when installing the MySQL server as reasonable as possible (see too much to completely use the default configuration installation), Choose a reasonable hardware configuration based on the application load. 1. P

= rcvlbes.customer_id and rcvblls.balance>0 ORDER by Cust.name Into TEMP cust_with_balance Then query in the temporary table in the following way: SELECT * from Cust_with_balance WHERE postcode> "98000" The rows in the staging table are less than the rows in the primary table, and the physical order is the required order, reducing disk I/O, so the query effort can be significantly reduced. Note: Changes to

type: ALL means) and does not use any indexes. This is a scan of tens of thousands of rows of records on the table. In an external query, each row is queried once. Although no value is used in the query, the query is "optimized" to reference an external query. According to this analysis, the

records of the table is not suitable for direct use. A performance optimization method for limit paging problemSpeed up paged queries with table overlay indexesAs we all know, if you only include that index column (overwriting index) in the statement that uses the index query, then this will query quickly. Because the index is used to find the

Optimization Methods for mysql nested queries and table queries: bitsCN.com poor optimization of nested queries As mentioned above, join table queries are more effective than nested queries without special considerations. Although the two queries share the same meaning, even though your plan is to tell the server what to do and then let it decide how to do it, sometimes you have to tell it how to change it.

Optimization objectivesReduce IO timesIo is always the easiest place to bottleneck the database, which is determined by the responsibility of the database, most of the database operations over 90% of the time is occupied by IO operations, reducing IO times is the first priority in SQL optimization, of course, is the most obvious optimization method.Reduce CPU Com

Simple MySQL optimization tool-slow query and mysql optimization tool Slow Query First, enabling slow queries is a prerequisite regardless of the optimization. The slow query Mechanism records slow

Nesting Queries Poor optimization As I mentioned above, a table query is more efficient than a nested query, regardless of the particular situation. Although the two queries express the same meaning, although your plan is to tell the server what to do and then let it decide what to do, sometimes you have to tell it to change. Otherwise the optimizer might do some

Poor Optimization of nested queriesAs mentioned above, join table queries are more effective than nested queries without special considerations. Although the two queries share the same meaning, even though your plan is to tell the server what to do and then let it decide how to do it, sometimes you have to tell it how to change it. Otherwise, the Optimizer may be stupid. I have encountered such a situation recently. These tables have three levels of h

Single-Table query optimization: (about the index, after the opening of a single chapter explained)(0) You can use the EXPLAIN keyword first to let you know how MySQL handles your SQL statements. This can help us to analyze the performance bottleneck of the query statement or the table structure.(1) Write SQL to specify the required fields, how many fields to wri

cust_with_balanceThen query in the temporary table in the following way:SELECT * from Cust_with_balanceWHERE postcode> "98000"The rows in the staging table are less than the rows in the primary table, and the physical order is the required order, reducing disk I/O, so the query effort can be significantly reduced.Note: Changes to the primary table are not reflected when the staging table is created. When d

Oracle query optimization and oracle Optimization 1. Reasonably sort query Conditions Oracle uses the bottom-up sequence to parse WHERE data. From the perspective of performance optimization, we recommend that you write the conditions that can filter out a large number of re

The MySQL user can perform. The system administrator who can control the MySQL server or computer can perform additional optimization measures. For example, some server parameters are attached to the query processing process and can be adjusted, and some hardware configuration factors have a direct impact on the query processing speed. In many cases, these optimi

When you submit a query, MySQL will analyze it to see if some optimization can be done to make it faster to process the query. This section describes how the query optimizer works. If you want to know the optimization methods used by MySQL, you can refer to the MySQL Referen

Basic query optimization and subquery Optimization in Oracle databases 1. Reasonably sort query Conditions Oracle uses the bottom-up sequence to parse WHERE data. From the perspective of performance optimization, we recommend that you write the conditions that can filter out