Quote:
I too believed that "showing" a table simply meant doing a "select..." .


It does. It's just that different queries will be optimised differently.

If you do a "SELECT ... WHERE ...", then the query optimiser will attempt to use any relevant indexes that it can find.

If you do a "SELECT * FROM T", then there's no point in using an index (since you're asking for all of the rows, there won't be any speedup). The query optimiser will do a simple table scan, which doesn't use any of the indexes.

This means that, depending on the exact query, and on the volume (and distribution) of data, the query optimiser can do entirely different things in order to find your data.
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-- roger