Quick & Easy SQL Tips
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This document provides SQL performance tips aimed at new database administrators, emphasizing quick fixes and best practices for optimizing SQL applications without extensive rewrites. Key topics include identifying performance bottlenecks, efficient memory management, indexing strategies, and using common table expressions. The document concludes with resources for further learning and emphasizes the importance of enforcing business rules and avoiding resource-intensive operations.
![Tip #8 - Quick Indexing Tricks.check for clustered indexesSELECT t.[Name] FROM sys.Indexes i JOIN sys.Tables t ON t.Object_ID = i.Object_id WHERE i.type_desc = 'HEAP' ORDER BY t.[Name]check for nonclustered indexes on foreign key columns (ID Columns)select * from sys.columns c where c.name like '%id%' and c.object_id not in ( select object_id from sys.index_columns )check for non-clustered covering indexesreads outnumber inserts/updates 5 to 10 to 110](https://image.slidesharecdn.com/quickeasysqltips-110919075135-phpapp01/85/Quick-Easy-SQL-Tips-10-320.jpg)
Quick & Easy SQL Tips
- 1. Quick & Easy SQL TipsIke Ellishttp://www.ellisteam.netike@ellisteam.netTwitter: @ike_ellis1
- 2. Assumptions @ YouYou are a new DBAYou don’t want to rewrite your entire application with a new schema, new DAL, or new queriesYou want to learn just enough so that your SQL apps are fast and maintainable2
- 3. Tip #1 – Performance Problem: Check the low-hanging fruit Long-running jobsLong-running transactionsDBCC OPENTRANCheck for long-running queries/both in amount and in duration3
- 4. Tip #2: Prettify!4http://extras.sqlservercentral.com/prettifier/prettifier.aspx
- 5. Tip #3 – Performance Problem : Identify hardware performance bottlenecks.MemoryDisk*ProcessorNetwork I/O*Most common bottleneck. It’s the Disk I/O, Stupid. (But it could be memory that’s causing it.)5
- 6. Tip #4: The right way to find hardware problemsMerging PerfMon and TracingGet the Batch and Completed Events OnlyNever trace from the computer you are monitoringAlways trace to a file and then load in a table after.6
- 7. Tip #5: Files, Files EverywhereAll need their own physical drive for space management and performanceMaster Data File (MDF)Log Files (LDF)TempDB FilesO/S/SQL FilesBAK Files7
- 8. Tip #6: The Log FileFills sequentially, so no need for striping, mirror is fine.Don’t let it get filled up: Simple Mode or Backup.8
- 9. Tip #7 - Good memory managementCheck for other applications running on the SQL ServerMove anti-virus (or at least make sure it wasn't scanning the SQL ports or the SQL files)Move Exchange and F&P services (cluster)Turn off unneeded servicesSQL is I/O bound, so I would turn off any network/disk intensive services (DHCP, DNS, etc)9
- 10. Tip #8 - Quick Indexing Tricks.check for clustered indexesSELECT t.[Name] FROM sys.Indexes i JOIN sys.Tables t ON t.Object_ID = i.Object_id WHERE i.type_desc = 'HEAP' ORDER BY t.[Name]check for nonclustered indexes on foreign key columns (ID Columns)select * from sys.columns c where c.name like '%id%' and c.object_id not in ( select object_id from sys.index_columns )check for non-clustered covering indexesreads outnumber inserts/updates 5 to 10 to 110
- 11. Tip #9 - Run the Index Tuning Wizard (DB Tuning Advisor)Run it a really long time, it is more accurate the longer it runsDon’t drop existing objectsIt’s OK to over-index11
- 12. Tip #10 – I don’t really know the symptoms, but SQL Doctor will find the cure.IderaRed GateDB ArtisonQuest12
- 13. Tip #11– Baseline the right wayIdera Diagnostics Manager & RedGate13
- 14. Tip #12 – Enforce Business Rules in the DBForeign KeysUnique ConstraintsCheck Constraints14
- 15. Tip #13 - Eliminate CursorsCursors focus on how, not why or whatCursors are expensiveCursors take up memory, which is usually a problem alreadyCursors can often be written using a set-based method15
- 16. Easy Tip #14 - Avoid Deadlocking, BlockingIndex TuneKeep transactions shortDon’t lock when you don’t have toHit the tables in the same order (create a table order document)Minimize the use of triggers16
- 17. Tip #15: CTE’sA named temporary result set based on a SELECT queryCommon Table ExpressionResult set can be used in SELECT, INSERT, UPDATE, or DELETE
- 18. Advantages of common table expressions:
- 19. Queries with derived tables become more readable
- 20. Provide traversal of recursive hierarchiesWITH TopSales (SalesPersonID, NumSales) AS( SELECT SalesPersonID, Count(*) FROM Sales.SalesOrderHeader GROUP BY SalesPersonId )SELECT * FROM TopSales WHERE SalesPersonID IS NOT NULLORDER BY NumSales DESC
- 21. Tip #16: apply operatorright parameter can be a table, but meant for tvfcross apply does inner joinno output for row when udf produces no outputudf can get its parameters from left inputouter apply does left outer joinall rows from left input returnedmay have nulls for columns returned by udf
- 22. Tip #17: temptables vs. table variablestable variables
- 23. private to batch
- 25. designed for smaller number of rows where scans are cheaper than seeks
- 26. limited indexing
- 27. static nature reduces recompiles
- 28. prefer to use with small number of rows
- 29. temporary tables
- 31. can be shared over sessions and scopes
- 32. can participate in transactions
- 33. can be indexed
- 34. can trigger frequent recompiles
- 35. get statistics
- 36. prefer to use when you have more rows
- 37. buffering data locallyTip #18: where exists vs. where inprior to sql server 2000, exists was preferred over innow they generate the same query planselect salesPersonIDfrom sales.salesPerson swhere exists(select managerIDfrom humanresources.employee ewhere e.managerID = s.salesPersonID)select salesPersonIDfrom sales.salesPersonwhere salesPersonID in(select managerIDfrom humanresources.employee)
- 38. where not exists vs. where not inthe possible presence of a null generates different plans for not exists and not inselect salesPersonIDfrom sales.salesPersonswhere not exists(select managerID fromhumanresources.employee ewhere e.managerID =s.salesPersonID)select salesPersonIDfrom sales.salesPersonwhere salesPersonID not in(select managerID fromhumanresources.employee)
- 39. Tip #19: Statistics Update22From the query plan, estimated number of rows and the actual number of rows need to equal each other. If they don’t, you might have a statistics issue.Run sp_updatestats to rectify it.
- 40. Tip #20: Big Rows from Query PlanWhen troubleshooting, thick rows means lots of data, thin rows mean not much data. You’re probably better off following the thick rows.23
- 41. Tip #21: Missing Index DetailsJust copy that, name the index something unique, and then run it. Remember, it doesn’t look for overlapping indexes, so check that before you run.24
- 42. ConclusionHave a great code camp!Ike Ellisike@ellisteam.net619.922.9801Twitter: @ike_elliswww.ellisteam.net25
Editor's Notes
- #4: DBCC OPENTRANselect s.plan_handle , t.text , sum(s.execution_count) as totalExecutionCount , sum(s.total_elapsed_time) as totalElapsedTime , sum(s.total_worker_time) as totalWorkerTime , sum(s.total_logical_reads) as totalLogicalReads , sum(s.total_logical_writes) as totalLogicalWrites from sys.dm_exec_query_stats s cross apply sys.dm_exec_sql_text(s.plan_handle) t group by s.plan_handle, t.text order by sum(s.execution_count) desc
- #5: Case Statements, bad code, etc.
- #15: Watch the actual execution plan for these statements:drop table dbo.t1drop table dbo.t2--create two test tablescreate table dbo.t1(c1 int, c2 int check(c2 between 10 and 20));insert into dbo.t1values (11,12);create table dbo.t2(c1 int, c2 int);goinsert into dbo.t2values(101, 102);go select t1.c1 , t2.c2 , t2.c2 from dbo.t1 join dbo.t2 on t1.c1 = t2.c2 and t1.c2 = 20;select t1.c1 , t1.c2 , t2.c2 from dbo.t1 join dbo.t2 on t1.c1 = t2.c2 and t1.c2 = 30;
- #18: A common table expression (CTE) can be thought of as a temporary result set that is defined within the execution scope of a single SELECT, INSERT, UPDATE, DELETE, or CREATE VIEW statement. A CTE is similar to a derived table in that it is not stored as an object and lasts only for the duration of the query. Unlike a derived table, a CTE can be self-referencing and can be referenced multiple times in the same query.A CTE is made up of an expression name representing the CTE, an optional column list, and a query defining the CTE. After a CTE is defined, it can be referenced like a table or view can in a SELECT, INSERT, UPDATE, or DELETE statement. A CTE can also be used in a CREATE VIEW statement as part of its defining SELECT statement. A CTE can be used to: Create a recursive query.Substitute for a view when the general use of a view is not required; that is, you do not have to store the definition in metadata.Enable grouping by a column that is derived from a scalar subselect, or a function that is either not deterministic or has external access.Reference the resulting table multiple times in the same statement.ReferencesUsing Common Table Expressions: http://go.microsoft.com/fwlink/?LinkID=127330