視圖上奇怪的Mysql查詢性能

Question

我有一個觀點：vcompanyendofday

以下查詢僅需0.7秒即可執行

Select * from vcompanyendofday

但是此查詢的條件很簡單，大約需要200.0秒

select * from vcompanyendofday where companyid <= 51;

這是視圖定義：

 CREATE VIEW `vcompanyendofday` AS 
  select  `c`.`companyid` AS `companyid`,
          `c`.`scripcode` AS `scripcode`,
          `e`.`eoddate` AS `eoddate`,
          `e`.`prevclose` AS `prevclose`,
          `e`.`delqty` AS `delqty` 
  from    (
          `company` `c`
  left join
          `endofday` `e`
  on      ((`c`.`companyid` = `e`.`companyid`)))
  where   (`e`.`eoddate` =
          (
          select  max(`e2`.`eoddate`) AS `max(eoddate)`
          from    `endofday` `e2` 
          where (`e2`.`companyid` = `c`.`companyid`)
          )
  );

Answer 1

似乎您在endofday.companyid上沒有索引

添加條件后， company將成為連接的領導者，並扼殺所有性能。

在endofday.companyid上創建索引：

CREATE INDEX ix_endofday_companyid ON endofday(companyid)

順便說一句，如果您想退回所有公司，則需要將子查詢放入OUTER JOIN的ON子句中，否則您丟失的endofday將會被過濾掉：

CREATE VIEW `vcompanyendofday` AS 
select  `c`.`companyid` AS `companyid`,
        `c`.`scripcode` AS `scripcode`,
        `e`.`eoddate` AS `eoddate`,
        `e`.`prevclose` AS `prevclose`,
        `e`.`delqty` AS `delqty` 
from    (
        `company` `c`
left join
        `endofday` `e`
on      `c`.`companyid` = `e`.`companyid`
        AND `e`.`eoddate` =
        (
        select  max(`e2`.`eoddate`) AS `max(eoddate)`
        from    `endofday` `e2` 
        where (`e2`.`companyid` = `c`.`companyid`)
        )

Answer 2

您是否嘗試過使用WHERE子句自己創建視圖的選擇，看看會發生什么？

如果發生此問題，請對該查詢運行EXPLAIN以查看發生了什么。

猜測，其中一張表中沒有公司索引的索引，很可能是在最后一天。