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dikT
V2EX  ›  程序员

PSQL 查询耗时问题

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  •   dikT · Apr 11, 2017 · 2483 views
    This topic created in 3339 days ago, the information mentioned may be changed or developed.

    下面两个语句

    sql> SELECT * FROM ***.trade_record ORDER BY id LIMIT 10 OFFSET 999999
    [2017-04-11 11:16:34] 10 rows retrieved starting from 1 in 341ms (execution: 318ms, fetching: 23ms)
    
    
    sql> SELECT id FROM ***.trade_record ORDER BY id LIMIT 1 OFFSET 999999
    [2017-04-11 11:16:56] 1 row retrieved starting from 1 in 7s 691ms (execution: 7s 688ms, fetching: 3ms)
    

    请问为啥查询数量少,字段少的 反而消耗的时间多呢

    execution: 执行

    fetching: 获取么?..

    为啥差距这么大呢

    2 replies    2017-04-11 12:45:48 +08:00
    sagaxu
        1
    sagaxu  
       Apr 11, 2017
    EXPLAIN 看一下查询计划
    prasanta
        2
    prasanta  
       Apr 11, 2017
    我也比较关心这个问题
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