Table structure for config
:
- property (primary key)
- value
- description
Query:
SELECT property, value FROM config
If I put a covering index on (property, value)
the optimizer still chooses the PRIMARY
index, but the extra
in EXPLAIN
is NULL
. If I tell the optimizer to use my covering index, the extra
in EXPLAIN
is USING INDEX
.
What’s really happening here? Why is the optimizer choosing the PRIMARY
index over my covering index by default? Am I avoiding disk IO by telling the optimizer to use my covering index?
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