steps to optimize sql query

In programming languages with large numbers, the code is processed in the encoding order, but in SQL, the first clause to be processed is the FROM clause. Although the first SELECT statement appears, but it is almost always processed.Each step generates a virtual table, which is used as the input for the next step. These virtual tables are unavailable to callers (client applications or external queries. Only the table generated in the last step will b

practical use, only in two tables connected with the restrictions, it will have practical significance, the following see the inner connectionInternal connectionIf it is understood in steps, the inner connection can be considered as a cross-linking of two tables, and then by adding a restriction (in SQL through the keyword on) to exclude a subset of the rows that do not meet the criteria, the result is an

on the disk, the only data we can control is the number of logical reads required to obtain the query results.Therefore, in the query performance adjustment, we can safely ignore the Physical Read value provided by the set statistics io command. (One way to reduce the number of physical reads and speed up the running of SQL Server is to ensure that the physical

Analyze the 48 causes of slow SQL query. There are many reasons for slow query speed. The following are common causes: 1. No index or no index is used (this is the most common problem of slow queryProgramDesign defects) 2. Low I/O throughput, resulting in a bottleneck effect. 3. the query is not optimized beca

Slow SQL query speedThere are many reasons for slow query speed in SQL Server databases. The following are common causes: 1. No index or no index is used (this is the most common problem of slow query and is a defect in programming) 2. Low I/O throughput, resulting in a bott

MySQL indexing principle and slow query optimization http://blog.jobbole.com/86594/Detail MySQL Index https://www.cnblogs.com/chenshishuo/p/5030029.htmlThe difference between MySQL's btree index and hash index https://www.cnblogs.com/vicenteforever/articles/1789613.htmlThe differences and applicability of several index types of MySQL https://www.cnblogs.com/yuan-shuai/p/3225417.htmlSlow query analysis MySQL

split the table to reduce the table size (sp_spaceuse)3. upgrade hardware4. Create an index based on the query conditions, optimize the index, optimize the access mode, and limit the data volume of the result set. Note that the fill factor should be appropriate (preferably the default value 0 ). The index should be as small as possible. Use a column with a small

, and query 4, the query can only be completed by indexing IX_UserName, without the need to perform a bookmarked search. Now let's take a look at the overhead and query plan of these two queries. We can see that we do not need to prompt the index. The query optimizer has automatically selected our index, logical reads

(Sp_spaceuse).3, upgrade the hardware.4, according to the query criteria, index, optimize the index, optimize access mode, limit the data volume of the result set. Note that the fill factor is appropriate (preferably using the default value of 0). The index should be as small as possible, using a Lie Jian index with a small number of bytes (refer to the creation

Users with(index(IX_UserName)) where UserName like 'ja%' For more information about Include, see the include charm in SQL Server indexes (indexes with contained columns) It is explained that the bookmarked search has a great impact on the query performance and is basically inevitable. This does not mean that the bookmarked search is a great beast. We didn't know what a bookmarked search is, the

= 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

(IX_UserName)) where UserName like 'ja%' For more information about Include, see the include charm in SQL Server indexes (indexes with contained columns) It is explained that the bookmarked search has a great impact on the query performance and is basically inevitable. This does not mean that the bookmarked search is a great beast. We didn't know what a bookmarked search is, the