how to optimize sql query using execution plan

Say something about the SQL Server execution plan, first of all I'm not a DBA, and I've done some things about SQL optimization in the last few years, and there's something that I understand, and that's not necessarily true. The difference between the T-SQL statement and the

the same value, re-test after rebuilding the index UPDATE _t SET c = ' 10100 ' WHERE c >= ' 10100 ' and C ' 11000 'ALTER INDEX ix_c on _t REBUILD; GO SET showplan_all onGOSELECT * from _t WHERE c = N' 10005 '; GO SET showplan_all OFF; Accordingly, the estimated number of rows is also increasing If we use the correct data type, where C = ' 10005 ', you can always get the correct estimated number of rows.I'm not sure what criteria SQL server uses

of the query, and if there are no indexes in the query or too many rows to scan, you can feel a noticeable delay. Therefore, you need to change the query mode or create a new index. The explain syntax in MySQL can help us rewrite queries, optimize the structure of tables and set up indexes to maximize

aggregation scan and the table scan actually the difference is not big, must say the difference is large, also must see what in the condition is what, later returns the data. In the case of this SQL statement, the efficiency difference is not very large. You can look at the I/O statistics: Table Scan: 　　 Clustered Index Scan: 　　 This is beyond the scope of this article, the efficiency is not in the context of this article, this article only consider

When optimizing SQL Performance, we often use viewing the execution evolution. The simplest thing is to use Ctrl + L to view the execution plan, however, the first time I saw this interface, my friends may not be able to get started. SQL server uses icons to display the

1.php Execution Time:$begin=Microtime(true);//gets the time that the program started executing//some code here to execute$stop=Microtime(true);//gets the time that the program execution endedList($m 0,$s 0)=Explode(" ",$begin);List($m 1,$s 1)=Explode(" ",$stop);$runtime=($s 1+$m 1-$s 0-$m 0) *1000;Echo' $etime-$stime.‘ microseconds; 2.SQL

(1) Try to select smaller columns;(2) to index the more frequent fields in where;(3) Avoid using * in select;(4) Avoid the use of calculations, not-in and (5) Use limit1 when only one row of data is needed;(6) To ensure that the single-table data does not exceed 200w, real-time partition table;For a slow query, you can use explain to analyze the statement's specific execution.How do you describe how

Empno,ename,category from emp WHERE empno = ' 7369 'Instead of using the SELECT * from emp WHERE empno = ' 7369 ' 9. Sorting Avoid the use of resource-intensive operations, SQL statements with Distinct,union,minus,intersect,order by will start the SQL engine execution, resource-intensive sorting (sort) fu

This article follows: SQL Server execution Plan operator detailed (1)-Assertion (Assert)Objective:According to the plan, this article began to tell the other operator concatenation (concatenation), the reader can be based on the word (both English and Chinese) first fantasy is what it is. In fact, it is very intuitive,

Knowledge Popularization: 1 normally, we use the explain plan for, set autotrace, and utlxplan methods to view the execution plans. They are all the execution plans generated by optimizer and do not fully conform to the execution paths of Oracle internal SQL statements. 2

ArticleDirectory 1. Example of replacing inner join with exists: When using exists, if you can use it correctly, it may increase the query speed: 1. Replace inner join with exists 2. Replace in with exists 1. Example of replacing inner join with exists: When writing SQL statements, you may encounter the following statements: When two tab

Hive provides an explain command that shows the execution plan for a query. The syntax for this statement is as follows: EXPLAIN [EXTENDED] query Hive> explain select a. Bar, count (*) from invites a where a. Foo> 0 group by A. bar; OKAbstract syntax tree:(Tok_query (tok_from (tok_tabref (tok_tabname invites) A) (to

Switching-Different SQL Plan with SQL profiles in Oracle ... When SQL is generated dynamically by a business system, or is generated by a third-party system, it may be difficult to modify the business program to improve execution pl