What to keep in mind?
- Avoid using functions in WHERE clause on indexes when it is not needed
- Use LIMIT when partial results are needed
- Order of columns in Multi-Column Indexes is important
- Extra conditions in WHERE clause can ruin the use of index-only scan, which doesn't access the actual table at all. Even if the filter limits the results more, it requires more processing
- Use LIKE filters wisely as explained in the previous idea
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Single vs Concatenated Indexes
Terminology:
- Single Index = Single-Column Index
- Concatenated Index = Multi-Column Index
How indexes work:
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Order in Multi-Column Index Matters
Order of the columns matter.
The index is useless if the first column doesn't appear in the WHERE clause.
Example 1:
An index on (t, x) will not be used in this query:
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