query optimization in dbms

MySQL Query optimization lecture administrator's optimization measures the optimization measures described in the previous section are not executed by privileged MySQL users. The system administrator of the MySQL server or computer can perform additional optimization measure

Table_rows query optimization and table_rows Optimization In daily application O M, Dev or db must calculate the number of rows in the table to serve as an information reference for the application or maintenance. Many may ignore the impact of SQL statements similar to select count (*) from table_name on database performance, but you can see that the execution h

basic operations for queries 1. The selection action corresponds to a constraint, and the Action object is a row of a two-dimensional table. Optimization mode: Select the operation of the push purpose: Minimize the number of yuan rental before the connection operation, so that the intermediate temporary relationship as small as possible (less than the number of tuples, the number of tuples to be connected) benefits: This may reduce IO and CPU consump

First of all, let's look at one of the steps here that translates into banner, which requires pivot, step-by-step Then look at the overall query results for the two query methods after the main table join So take a look at the latter query method is also through the industry after the conversion to do the join execution plan, you can see only the Word table

WHERE rental_date=‘2006-02-14 15:16:03‘ AND customer_id >= 300 AND customer_id 400; Type=ref, indicating that the index was used. 7. Column name is index, COLUMN_NAME is null, using index SELECT * FROM payment WHERE rental_id IS NULL; typical scenario where an index exists but cannot use an index 1. A like query that starts with% SELECT * FROM actor WHERE last_name LIKE ‘%NI%‘; #优化 SELECT * FROM (SELECT actor_id FROM actor WHERE last_name LIKE ‘%NI

null value, and then query: Select ID from t where num = 0 (3) In and not in also to use caution, otherwise it will result in a full table scan, such as: For consecutive values, you can use between instead of in: A lot of times it's a good choice to replace in with exists: (4) Try to use a numeric field, if the field containing only numeric information should not be designed as a character type, which will reduce the performance of

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

Here we will mainly introduce you to DB2 Performance Tuning: Design and configure the Use constraints of your database solution to improve query optimization, we all know that many database design and configuration options can affect query performance. For more suggestions on Database Design, see the "Planning your Physical Database Design" Best Practices article

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

MySQL Optimization-query and mysql Optimization Reprinted please indicate the source: http://blog.csdn.net/l1028386804/article/details/46580589 Basic select syntax in MySQL Select attribute list from Table Name and View list [where condition expression] [group by attribute name [having condition expression] [order by attribute name [asc | desc] [limit Note: Wh

, but in fact each server has only one member table and a distributed partition view. The data location is transparent to the application.11. Rebuild the index dbcc reindex, dbcc indexdefrag, shrink data and log dbcc shrinkdb, and dbcc shrinkfile. set automatic log shrinking. for large databases, do not set Automatic database growth, which will reduce the server performance. The writing of T-SQL is very important. The following lists common points: first, the process of

; CREATE VIEW Trade_detail as SELECT * FROM Trade_detail_1 UNION ALL SELECT * to trade_detail_2 UNION ALL SELECT * From Trade_detail_3 UNION ALL SELECT * from Trade_detail_4; This allows you to access only the small tables when querying for data in a certain period of time, and you can also conduct federated queries when needed. Oracle Query Optimization Four aspects: SQL

server has a copy of the original table, but in fact each server has only one member table and a distributed partition view. The data location is transparent to the application. 11. Rebuild the index DBCC reindex, DBCC indexdefrag, shrink data and log DBCC shrinkdb, and DBCC shrinkfile. set automatic log shrinking. for large databases, do not set Automatic database growth, which will reduce the server performance. The writing of T-SQL is very important. The following lists common points: first,

MySQL query too slow is a very annoying thing, so, the author has spent some time to organize the MySQL Query speed optimization program, this article is all the author's personal views, such as questions or wrong welcome to communicate and correct, we learn together progress. Count () Optimization for MySQL large tab

It is well known that in today's popular enterprise architecture, ORM has always been the most basic part, at the bottom of the architecture design, providing object-oriented operational support to the logical layer, and the fact is always biased with our expectations, ORM in providing a better operating experience, also lost a part of native SQL flexibility and efficiency, Of course, this problem does not affect our use of ORM framework, but it hinders our website traffic, especially in the ent

Let's first review the basic knowledge of field selectivity. -- Basic knowledge of field selectivity -- Introduction: Can I create indexes for all fields? As shown in the following table, the sort field has very poor selectivity. You can run the show index from ads command to see that sort's Cardinality (hash level) is only 9, and this field should not be indexed: Table Non_unique Key_name Seq_in_index Column_name Collation Cardinality Sub_part Packed Null

name to run on any member server. The system operates as if each member server has a copy of the original table, but there is only one member table and one distributed partitioned view on each server. The location of the data is transparent to the application.11. Rebuild the index DBCC REINDEX, DBCC INDEXDEFRAG, shrink data and log DBCC SHRINKDB,DBCC shrinkfile. Sets the auto-shrink log. For large databases do not set the database autogrow, it will degrade the performance of the server. There's

in my last Post, " " Java " Itoo the actual project Hibernate Lazy Load Optimization Performance "I have mentioned that student data has 2 million, query data is very slow, this is a very difficult thing to see the page progress bar has been rotating circles, the feeling of anxious really can't describe. The first consideration was to use lazy to optimize, because the foreground frame reason,lazy

tables. 25. Avoid using cursors as much as possible, because 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 preferabl

SQLite is a typical embedded DBMS with many advantages. It is lightweight and small after compilation. One of the reasons is that it is relatively simple in query optimization, it only uses the index mechanism for optimization. After the analysis of the SQLite query