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SQL Tips + Tricks for Developers
- 1. Lunch + Learn SQL Tips + Tricks for Developers Victor Szoltysek July / 2016
- 4. Not closing resources • always using finally block / try-resources finally{ sql1.close(); sql2.close(); } @Cleanup Resource someClosableResource;
- 5. Missing Indexes • Not important for small tables • Huge potential performance improvements — x10000 • Watch out for incorrect index usage • MSSQL Server will recommend indexes • ORMs don’t create indexes!!!! SELECT * FROM someTable WHERE someColumn LIKE ‘%stringInMiddle%’
- 8. SQL Injection - Mitigation • Never EVER use concatenated SQL strings in your prod applications • Use Parametrized Statements
- 9. Not using Transactions when Needed • Transaction : • Logical Atomic Unit of Work • All or nothing (even if database gets interrupted) • Solution for A/B • Spring @Transactional Annotation
- 10. Null misunderstandings! • NULL == NULL <— not true • NULL != NULL <— also not true • NULL != “something” <— ALSO not true • Empty Strings become Null in Oracle!!
- 11. N+1 AntiPattern • Minimize SQL Traffic!! , Let SQL perform joins, Network is slow • Use SQL Count instead of getting all rows and counting at backend -- Get all Mobile Vendors SELECT * FROM MobileVendor; -- For each MobileVendor, get PhoneModel details SELECT * FROM PhoneModel WHERE MobileVendor.vendorId=?
- 12. Stale Statistics • Database keeps track of statistics about table data to help to optimize how it executes queries • Significant changes to data, can make these statistics temporarily invalid, and can lead to poor execution • Only important with large DB changes, i.e. full refresh
- 13. Tools
- 14. Spring Data - Auto Generated Repositories
- 15. Intellij Ultimate SQL Support
- 16. VirtualBox + Windows + SQL Server Express + Mangement Studio
- 18. Different SQL Databases SQL Server Oracle Postgres MySQL Firebird H2 Single Cross Platform Deployable No No No No No Yes Embedded Support No No No No Yes Yes InMemory Support No No No Yes No Yes Free No No Yes Yes Yes Yes Cross Platform No Yes Yes Yes Yes Yes
- 19. InMemory / Embedded / Java Databases String connectionString = "jdbc:h2:mem:inMemoryDb;DB_CLOSE_DELAY=-1" Awesome for Testing!!!
- 20. Most commonly used SQL database?
- 21. Explain Plans
- 24. ORMs • Great for Greenfield / CRUD apps • Easy to go from Object Model to SQL Model • Can get difficult to create Object Model from existing SQL Model • “ORMS are the Vietnam of Computer Science”
- 25. NoSQL vs SQL vs NewSQL • NoSQL did not replace SQL, but is an alternative • Relational / Structured Data is still create for SQL DB’s • NewSQL!! Modern SQL alternatives
- 27. SQL Metadata SELECT t.NAME AS TableName, p.rows AS RowCounts, (SUM(a.total_pages) * 8 / 1064) AS TotalSpaceMB FROM sys.tables t INNER JOIN sys.schemas s ON s.schema_id = t.schema_id INNER JOIN sys.indexes i ON t.OBJECT_ID = i.object_id INNER JOIN sys.partitions p ON i.object_id = p.OBJECT_ID AND i.index_id = p.index_id INNER JOIN sys.allocation_units a ON p.partition_id = a.container_id WHERE t.NAME NOT LIKE 'dt%' -- filter out system tables for diagramming AND t.is_ms_shipped = 0 AND i.OBJECT_ID > 255 GROUP BY t.Name, s.Name, p.Rows ORDER BY p.Rows desc
- 28. Table Analysis Table Row Count Size MB agreement_customer 1039293 103 pricing_results 378520 189 sales_history 378520 40 price_rule 256814 26 base_value 252687 19 customer 32754 3 product 19525 1 product_price 19525 5 agreement_product 15105 1 price_rule_flag 7656 0 price_rule_header 2552 0 min_max_rule 292 0 DATABASECHANGEL OG 61 0 sub_price_rule 29 0