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My MySQL SQL Presentation
Indexes are used to efficiently retrieve data from MySQL tables. The most common type is the B-Tree index, which allows quick retrieval of data by key and scanning in order. Indexes work by storing pointers to data rows, improving performance for queries that filter, join, group or sort by indexed columns. Good indexes are small, use minimal data types, and cover columns frequently queried, joined on or used for filtering, grouping and sorting.
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My MySQL SQL Presentation
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- 2. Most of ourdata lives in MySQL We want to get it as efficiently as possible How?
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- 4. Small tables? Notalways practical
- 5. Small tables? Notalways practical Indexes?
- 6. Small tables? Notalways practical Indexes? OK, but how?
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- 8. First things first: Whatare indexes used for?
- 17. How do indexeswork?
- 18. How do indexeswork? Storage Types
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- 21. BTree Ordered key-value map Mostcommon storage type
- 22. BTree Ordered key-value map Mostcommon storage type Quickly find a given key and can be scanned in order
- 23. BTree Ordered key-value map Mostcommon 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'
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- 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 indexeswork? Pointers
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- 48. Selectivity of acolumn is the ratio between the number of distinct values and the number of total values
- 49. Selectivity of acolumn 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
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- 51. Selectivity Tips Always aimfor >15%
- 52. Selectivity Tips Always aimfor >15% Joins on columns with low selectivity are expensive
- 53. Selectivity Tips Always aimfor >15% Joins on columns with low selectivity are expensive Watch out for columns like `status`, `gender`, and `active`
- 54. What makes agood index?
- 55. Small Use smallest datatype possible Consider partial indexes on varchar/char to increase selectivity
- 56. Filter Columns Try toidentify columns that will be used to filter data
- 57. Join Columns Identify columnsthat will often be joined on/to from other tables
- 58. Covering Indexes A querythat can use a covering index will be substantially faster than one that has to read from the table
- 59. Group/Sort Identify columns thatwill be used for grouping and sorting
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- 61. MySQL cannot usean index if the columns do not form a leftmost prefix of the index
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