This access algorithm is employed when the
WHERE
clause was converted to several range
conditions combined by OR
, but
for which the Index Merge method union algorithm is not
applicable.
Examples:
SELECT * FROMtbl_name
WHEREkey_col1
< 10 ORkey_col2
< 20; SELECT * FROMtbl_name
WHERE (key_col1
> 10 ORkey_col2
= 20) ANDnonkey_col
=30;
The difference between the sort-union algorithm and the union algorithm is that the sort-union algorithm must first fetch row IDs for all rows and sort them before returning any rows.
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