sql query optimization techniques

1. UseProgramTo minimize the number of accesses to the database. By searching for parameters, You can minimize the number of rows accessed to the table and the result set, thus reducing the network burden; separate operations should be processed separately to improve the response speed each time. When using SQL in the data window, try to place the indexes in the first column selected;AlgorithmThe structure should be as simple as possible; During the

is used, be sure to explicitly delete all temporary tables at the end of the stored procedure, TRUNCATE table first, and then drop table, which avoids longer locking of the system 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

Label:Database Design Aspects: 1, to optimize the query, should try to avoid full table scan, first of all should consider the where and order by the columns involved in the index. 2, should try to avoid the null value of the field in the Where clause to judge, otherwise it will cause the engine to abandon the use of the index for a full table scan.such as: Select ID from t where num is nullYou can set the default value of 0 on NUM, make sure that the

Tags: nbsp ati exist query multi-table Org Table Association 1.4 SeleSelect a from a a b where a.t=b.tSelect a from a-a where a.t in (select b.t from b b)Select distinct a.org_code,a.org_name from t_organzation a,t_dm_cdbp_organzation b where a.org_code=b.org_code;Select distinct a.org_code,a.org_name from T_organzation a where a.org_code in (select B.org_code from T_dm_cdbp_organzati on B);Select distinct a.org_code,a.org_name from T_organzation a wh

where num = 20 5. InAndNot inUse it with caution. Otherwise, full table scan may occur, for example:Select ID from t where num in (1, 2, 3)Continuous values can be usedBetweenDo not useInNow:Select ID from t where num between 1 and 3 6.The following query will also cause a full table scan:Select ID from t where name like '% ABC %'To improve efficiency, you can consider full-text search. 7. if you use parameters in the where clause, full ta

(user_lookups), if these two values are small, you might consider dropping the index.When you restart the SQL Server service, the various counters in the Sys.dm_db_index_usage_stats system view are initialized to null values. In addition, whenever data is detached or closed (for example, because Auto_Close is set to ON), all data rows associated with the database are deleted. When an index is first used, it is added to the system's statistics, and Sy

Multi-field fuzzy query SQL like % optimization and Difference Http://anforen.5d6d.com/ Select * From [klims]. [DBO]. [task] Where clientcompany like '% A %' or [address] Like '% A %' Select * From [klims]. [DBO]. [task] Where clientcompany + [address] Like '% A %' However, if one of the fields is null, data cannot be found in the second type. Http:

Label:1. Overview2. Database design Principles1) familiar with the requirements2) Develop a database that conforms to the specifications3) Audit Database designIn addition to auditing the logical issues in database design, the audit team should also focus on whether the data dictionary is detailed and understandable, whether the data table structure is redundant, and suggests changes.3. Database Design Code1) Naming conventions2) clarify the relationship between the entity and the data table3) A

overlay index becomes very wide, then you can consider an index connection.For this sentence SQL (select Username,gender from dbo. UserInfo where username= ' userN600 ' and gender=1 ' can build a nonclustered index on the Gender.For this example, it is possible that the SQL optimizer does not use both the nonclustered index ix_username and our newly established index on gender, so we can tell the

on a trace flag during a specific query run, or only disable one of the optimizer rules during query compilation by following an archive Querytraceon or Queryruleoff prompt.Select @v_test =c1from t1 where c1=2 option (Recompile,querytraceon 2389);Select @v_test =c1from t1 where c1=2 option (Recompile,queryruleoff omitmyidx);The syntax shown in the second statement above may result in a "no plan" error. Que

V_cust_rcvlbesWHERE postcode> "98000"The number of rows in the view is 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. 23, you can use distinct without GROUP bySELECT OrderID from Details WHERE UnitPrice > Ten GROUP by OrderIDCan be changed to:SELECT DISTINCT OrderID from Details WHERE UnitPrice > 10 24. Use UNION ALL to not use UnionUNION all

30 SQL query optimization tips for mysql with tens of millions of big data, mysqlsql 1. To optimize the query, try to avoid full table scanning. First, consider creating an index on the columns involved in where and order. 2. try to avoid null value determination on the field in the where clause. Otherwise, the engine

if the amount of data is small, create table to mitigate the resources of the system tables. Then insert. 24. If a temporary table is used, be sure to explicitly delete all temporary tables at the end of the stored procedure, TRUNCATE table first, and then drop table, which avoids longer locking of the system 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. 2

your entire site from stopping accordingly. Because these two operations will lock the table, the table is locked, the other operations are not in. Apache will have a lot of child processes or threads. So, it works quite efficiently, and our servers don't want to have too many child processes, threads and database links, which is a huge amount of server resources, especially memory. If you lock your watch for a period of time, say 30 seconds, then for a site with a high volume of traffic, the 3

procedure, TRUNCATE table first, and then drop table, which avoids longer locking of the system 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 tab

Tags: blog using io data problem div time SQLWhen you use a like fuzzy query in an SQL statement, you should try to avoid the percent of percent, because the fuzzy query is relatively slow, and when this happens, you should consider optimization.For example, I query a table for records created in 2012SELECT * from ' co

SQL data query optimization select nbsp;. id, rkno,. packageno nbsp; as nbsp; packageno, cust_no, lotno, count (*) nbsp; as nbsp; count nbsp; from nbsp; 'rk _ record ' SQL data query optimization Select. id, rkno,. package

cursors. If development time permits, a cursor-based approach and a set-based approach can all be tried to see which method works better. 28. Set NOCOUNT on at the beginning of all stored procedures and triggers, set NOCOUNT OFF at the end. You do not need to send a DONE_IN_PROC message to the client after each statement that executes the stored procedure and trigger. 29. Try to avoid large transaction operation and improve the system concurrency ability. 30. Try to avoid the return of large da

operation is the same as in 1, and the merge into method is recommended if you make a decision. Because merge into accesses only one emp_new1. Iii. Deleting delete operations 1. Delete duplicate records: There are many kinds of methods, here only one, using the analysis function grouping, determine whether the group number is greater than 1. Delete from emp where rowid in (select Rid from (select rowID as RIDs, row_num

Querying case-insensitive data in MySQL often uses subqueries and uses the upper function in a subquery to convert the condition to uppercase. Such as: The code is as follows:SELECT * FROM Staticcatalogue WHERE UPPER (source) in (select UPPER (source) to Staticcatalogue GROUP by UPPER (source) hav ing count (UPPER (source)) >1) Order by UPPER (source) DESC; The execution efficiency of this statement is very low, especially if the source field is not indexed. In particular, the most taboo to u