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explain select * from t1 force index(key1, key2) where key1 < 3 or key2 < 3;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t1 index_merge key1,key2 key1,key2 5,5 NULL 4 Using sort_union(key1,key2); Using where
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1 SIMPLE t1 index_merge key1,key2 key1,key2 5,5 NULL 5 Using sort_union(key1,key2); Using where
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select * from t1 force index(key1, key2) where key1 < 3 or key2 < 3;