Top Tips for Better T-SQL
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T-SQL provides many different ways to accomplish the same task, and as you might expect, some ways are better than others. Also, it's very simple to write your T-SQL in a way that no one else can read. In this session, you will learn specific techniques, that if followed, will make you a better T-SQL developer. The session is jam-packed with practical examples and is designed for administrators and developers who want to bring their T-SQL skills to the next level. You'll write clearer and easier to read T-SQL as well as write better performing T-SQL. In fact, you will be able to immediately implement these tips in your current projects once you get back to your office.
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Top Tips for Better T-SQL
- 1. Grant Fritchey | www.ScaryDBA.com www.ScaryDBA.com Top Tips for Better T-SQL Stored Procedures Grant Fritchey – Red Gate Software
- 2. Grant Fritchey | www.ScaryDBA.com Goal Learn methods for writingT-SQL for readability Understand how to write T-SQL for performance 2
- 3. Grant Fritchey | www.ScaryDBA.com Get in touch scarydba.com grant@scarydba.com @gfritchey Grant Fritchey
- 4. Grant Fritchey | www.ScaryDBA.com Agenda Writing for readability » Object Names & Format » Comments » Error Handling » Personal Preferences Writing for performance » DataTypes » Functions inComparisons » ImproperUse of Functions » The “Run Faster” Switch » InappropriateUse ofQuery Hints » Recompiles » Row byAgonizing Row » NestingViews 4
- 5. Grant Fritchey | www.ScaryDBA.com Writing for Readability Define a local standard » Object names » Comments » Format » Error handling Enforce the standard » Document it » Code reviews 5
- 6. Grant Fritchey | www.ScaryDBA.com Object Names & Format Names should be descriptive » Procedures should be a phrase » Abbreviations should be common (no Ddltbl) Use aliases » Clear » Common Be consistent » A foolish consistency is the hobgoblin of little minds » Keyword in that sentence is “foolish” 6
- 7. Grant Fritchey | www.ScaryDBA.com Comments Do something Most important is describing the action, not documentation Use source control for documentation Self-documenting code is a lie 7
- 8. Grant Fritchey | www.ScaryDBA.com Error Handling TRY/CATCH Deadlocks Establish local best practices 8
- 9. Grant Fritchey | www.ScaryDBA.com Personal Preferences CamelCase Uppercase for reserve words and key words Line breaks » On SELECT list » Between JOIN criteria » BetweenWHERE criteria Use the semicolon Indent » After initial SELECT » With ON clause » AfterWHERE clause 9
- 10. Grant Fritchey | www.ScaryDBA.com Writing For Performance Write for your data structures Write for your indexes Write for the query optimizer Avoid common issues: » Data types » Functions in comparisons » Improper use of functions » The “run faster” switch » Inappropriate Query Hints » Recompiles » NullValues » Row By Agonizing Row » NestedViews 10
- 11. Grant Fritchey | www.ScaryDBA.com Data Types Problem » Implicit or explicit data type conversion Indications » Scans » Slow performance Solution » Use appropriate data types 11
- 12. Grant Fritchey | www.ScaryDBA.com Functions in Comparisons Problem » Function on column in WHERE or JOIN criteria Indications » Scans » Slow performance Solution » Don’t run functions on columns » Use sargeable functions 12
- 13. Grant Fritchey | www.ScaryDBA.com Improper Use of Functions Problem » Multi-statement user defined functions cause poor performance Indications » Zero cost scan operator in exec plan » Very slow performance Solution » When working with more than a few (~50?) rows, don’t use them » When using operations such as JOIN that require statistics, don’t use them 13
- 14. Grant Fritchey | www.ScaryDBA.com The “Run Faster” Switch Problem » Use of the NO_LOCK query hint everywhere, or setting transaction isolation level to READ_UNCOMMITTED Indications » Extra rows in result set » Missing rows in result set Solution » Tune the queries » Tune the structures » Use snapshot isolation levels http://www.jasonstrate.com/2012/06/the-side-effect-of- nolock/ 14
- 15. Grant Fritchey | www.ScaryDBA.com Query Hints Problem » Query hints in the code such as FAST n, index hints, JOIN hints Indications » Inconsistent performance behavior » Bad performance » Odd looking execution plans Solution » Use of query hints should be exceptional » Exceptions are rare, not standard practice 15
- 16. Grant Fritchey | www.ScaryDBA.com Recompiles Problem » Excessive blocking and CPU contention caused by constant or long statement recompiles Indications » Recompile events in extended events or trace » Blocking » High CPU usage Solutions » Avoid interleaving DDL & DML » Where viable, use table variables 16
- 17. Grant Fritchey | www.ScaryDBA.com Row by Agonizing Row Problem » Cursors instead of set-based operations » WHILE loops instead of set-based operations » Multiple statements where 1 will do Indications » Extremely slow performance Solutions » Eliminate unnecessary row-by-row processing 17
- 18. Grant Fritchey | www.ScaryDBA.com Nested Views Problem » Views within views causes optimizer timeout Indications » Incredibly complex query plans for simple queries » Very poor performance Solutions » Don’t nest views » Materialize views 18
- 19. Grant Fritchey | www.ScaryDBA.com Writing for Readability Define a local standard » Object names » Comments » Format » Error handling Enforce the standard » Document it » Code reviews 19
- 20. Grant Fritchey | www.ScaryDBA.com Writing For Performance Write for your data structures Write for your indexes Write for the query optimizer Avoid common issues: » Data types » Functions in comparisons » Improper use of functions » The “run faster” switch » Inappropriate Query Hints » Recompiles » Row By Agonizing Row » NestedViews 20
- 21. Grant Fritchey | www.ScaryDBA.com Goal Learn methods for writingTSQL for readability Understand how to write TSQL for performance 21
- 22. Grant Fritchey | www.ScaryDBA.com Get in touch scarydba.com grant@scarydba.com @gfritchey Grant Fritchey
- 23. Grant Fritchey | www.ScaryDBA.com Questions? 24