My MySQL SQL Presentation
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Brief introduction to indexing within MySQL
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My MySQL SQL Presentation
- 2. Most of our data lives in MySQL We want to get it as efficiently as possible How?
- 4. Small tables? Not always practical
- 5. Small tables? Not always practical Indexes?
- 6. Small tables? Not always practical Indexes? OK, but how?
- 8. First things first: What are indexes used for?
- 17. How do indexes work?
- 18. How do indexes work? Storage Types
- 19. BTree
- 21. BTree Ordered key-value map Most common storage type
- 22. BTree Ordered key-value map Most common storage type Quickly find a given key and can be scanned in order
- 23. BTree Ordered key-value map Most common storage type Quickly find a given key and can be scanned in order Works well with ranges All records between 50 and 100 All records starting with 'R'
- 25. Other storage types RTree / Spatial Index - Identify 'close' values in 2+ dimensions - Useful for geographic databases
- 26. Other storage types RTree / Spatial Index - Identify 'close' values in 2+ dimensions - Useful for geographic databases Hash - Unordered key/value map - Faster than BTree, but terrible for ranges
- 27. How do indexes work? Pointers
- 28. Pointers
- 32. Index Types
- 33. Single column
- 34. Single column
- 37. Covering
- 38. Covering
- 39. Covering
- 40. Partial
- 41. Partial
- 42. Partial
- 43. Downsides?
- 47. Selectivity
- 48. Selectivity of a column is the ratio between the number of distinct values and the number of total values
- 49. Selectivity of a column is the ratio between the number of distinct values and the number of total values Primary Keys and Unique Columns Always Have Selectivity of 1
- 50. Selectivity Tips
- 51. Selectivity Tips Always aim for >15%
- 52. Selectivity Tips Always aim for >15% Joins on columns with low selectivity are expensive
- 53. Selectivity Tips Always aim for >15% Joins on columns with low selectivity are expensive Watch out for columns like `status`, `gender`, and `active`
- 54. What makes a good index?
- 55. Small Use smallest data type possible Consider partial indexes on varchar/char to increase selectivity
- 56. Filter Columns Try to identify columns that will be used to filter data
- 57. Join Columns Identify columns that will often be joined on/to from other tables
- 58. Covering Indexes A query that can use a covering index will be substantially faster than one that has to read from the table
- 59. Group/Sort Identify columns that will be used for grouping and sorting
- 61. MySQL cannot use an index if the columns do not form a leftmost prefix of the index
- 72. Slow query log
- 73. Slow query log
- 74. Slow query log
- 75. Explain
- 76. Explain
- 77. Explain