SQL performance explained : everything developers need to know about SQL performance

SQL Performance Explained helps developers to improve database performance. The focus is on SQL—it covers all major SQL databases without getting lost in the details of any one specific product. Starting with the basics of indexing and the WHERE clause, SQL Performance Explained guides developers through all parts of an SQL statement and explains the pitfalls of object-relational mapping (ORM) tools like Hibernate. Topics covered include • Using multi-column indexes • Correctly applying SQL functions • Efficient use of LIKE queries • Optimizing join operations • Clustering data to improve performance • Pipelined execution of ORDER BY and GROUP BY • Getting the best performance for pagination queries • Understanding the scalability of databases Its systematic structure makes SQL Performance Explained both a textbook and a reference manual that should be on every developer’s bookshelf. Covers all major databases: Oracle® Database, SQL Server®, PostgreSQL, MySQL What readers say “This book is definitively worth having in the company library.” — Joe Celko ............................................................................................ vi 1. Anatomy of an Index ...................................................................... 1 The Index Leaf Nodes .................................................................. 2 The Search Tree (B-Tree) .............................................................. 4 Slow Indexes, Part I .................................................................... 6 2. The Where Clause ......................................................................... 9 The Equality Operator .................................................................. 9 Primary Keys ....................................................................... 10 Concatenated Indexes .......................................................... 12 Slow Indexes, Part II ............................................................ 18 Functions .................................................................................. 24 Case-Insensitive Search Using UPPERor LOWER.......................... 24 User-Defined Functions ........................................................ 29 Over-Indexing ...................................................................... 31 Parameterized Queries ............................................................... 32 Searching for Ranges ................................................................. 39 Greater, Less and BETWEEN..................................................... 39 Indexing LIKEFilters ............................................................. 45 Index Merge ........................................................................ 49 Partial Indexes ........................................................................... 51 NULLin the Oracle Database ....................................................... 53 Indexing NULL....................................................................... 54 NOT NULLConstraints ............................................................ 56 Emulating Partial Indexes ..................................................... 60 Obfuscated Conditions ............................................................... 62 Date Types .......................................................................... 62 Numeric Strings .................................................................. 68 Combining Columns ............................................................ 70 Smart Logic ......................................................................... 72 Math .................................................................................. 77 3. Performance and Scalability ......................................................... 79 Performance Impacts of Data Volume ......................................... 80 Performance Impacts of System Load .......................................... 85 Response Time and Throughput ................................................. 87 4. The Join Operation ....................................................................... 91 Nested Loops ............................................................................ 92 Hash Join ................................................................................. 101 Sort Merge .............................................................................. 109 5. Clustering Data ........................................................................... 111 Index Filter Predicates Used Intentionally ................................... 112 Index-Only Scan ........................................................................ 116 Index-Organized Tables ............................................................. 122 6. Sorting and Grouping ................................................................. 129 Indexing Order By .................................................................... 130 Indexing ASC, DESCand NULLS FIRST/LAST...................................... 134 Indexing Group By .................................................................... 139 7. Partial Results ............................................................................ 143 Querying Top-N Rows ............................................................... 143 Paging Through Results ............................................................ 147 Using Window Functions for Pagination .................................... 156 8. Modifying Data .......................................................................... 159 Insert ...................................................................................... 159 Delete ...................................................................................... 162 Update .................................................................................... 163 A. Execution Plans .......................................................................... 165 Oracle Database ....................................................................... 166 PostgreSQL ............................................................................... 172 SQL Server ............................................................................... 180 MySQL ..................................................................................... 188 Index ............................................................................................. 193 v