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Which of these will make a query unable to use an index on a VARCHAR column?

A WHERE name LIKE 'abc%'
B WHERE name LIKE '%abc'
C WHERE name = 'abc'
D WHERE name > 'abc'

Answer

WHERE name LIKE '%abc'

A leading wildcard means the search cannot start from a known prefix, so the sorted B-tree cannot be traversed and a full scan is required.

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