测试表请参数,数据量为一千六百万.
常规方法
explain (analyze,verbose,costs,buffers,timing)
select min(objectid),max(objectid) from test;
--Execution time: 0.190 m
explain (analyze,verbose,costs,buffers,timing)
select min(objectid),max(objectid) from test where num=20;
--Execution time: 0.122 ms另类的方法
explain (analyze,verbose,costs,buffers,timing)
(select objectid from test order by objectid limit 1)
union all
(select objectid from test order by objectid desc limit 1);
--Execution time: 0.156 ms
explain (analyze,verbose,costs,buffers,timing)
(select objectid from test where num=20 order by objectid limit 1)
union all
(select objectid from test where num=20 order by objectid desc limit 1);
--Execution time: 0.094 ms
explain (analyze,verbose,costs,buffers,timing)
select objectid as min,(select objectid from test order by objectid desc limit 1) as max from test order by objectid limit 1;
--Execution time: 0.157 ms
explain (analyze,verbose,costs,buffers,timing)
select objectid as min,(select objectid from test where num=20 order by objectid desc limit 1) as max from test where num=20 order by objectid limit 1;
-- Execution time: 0.095 ms虽然提升不是很多,但性能就是从细节中扣出来的