SELECT count(column) slower than SELECT *

Question

Two simple queries:

• SELECT * FROM some_table WHERE some_column = 1

  Returns array with all the records, with columns and values. About 100K in total. Takes ~40ms to complete.

• SELECT COUNT(id) FROM some_table WHERE some_column = 1

  Returns just the record count value, same count as the query above. Takes 1 second!!

EXPLAIN QUERY PLAN tells me the same thing for both queries: that it's searching the table using index...

Am I missing something here? Why is getting the count slower than getting the actual records?

I really don't want to use the 1st query, because I just need the count, and fetching 100K records will surely use all available memory :(

EXPLAIN QUERY PLAN output:

query #1:

selectid    order   from    detail
0   0   0   SEARCH TABLE atts USING INDEX idxType (type=?)

query #2:

selectid    order   from    detail
0   0   0   SEARCH TABLE atts USING COVERING INDEX idxType (type=?)

Answer 1

因此，事实证明，这两个查询之间没有区别 - 因此，根本没有问题。

说到总体时间安排 - 显然您必须从玩具数据库转移到真实数据库。