0

谁能帮我优化这个查询？需要 15 秒。如果我将 WHERE 子句移动到连接本身，结果仍然相同。

SELECT
`users`.`employeeID` as `username`,
`users`.`firstName` as `fname`,
`users`.`lastName` as `lname`
FROM `enrollment`
INNER JOIN `users` ON `enrollment`.`employeeID` = `users`.`employeeID`
WHERE `enrollment`.`number` = [int]
AND
`enrollment`.`term` = [int]
AND
(
`enrollment`.`status` = 'E'
OR
`enrollment`.`status` = 'M'
)
ORDER BY    
`users`.`lastName` ASC,
`users`.`firstName` ASC;

只要这样：

SELECT
`users`.`employeeID` as `username`,
`users`.`firstName` as `fname`,
`users`.`lastName` as `lname`
FROM `enrollment`
INNER JOIN
`users` ON `enrollment`.`employeeID` = `users`.`employeeID`
AND
`enrollment`.`number` = [int]
AND
`enrollment`.`term` = [int]
AND
(
`enrollment`.`status` = 'E'
OR
`enrollment`.`status` = 'M'
)
ORDER BY    
`users`.`lastName` ASC,
`users`.`firstName` ASC;

这是解释结果

id  select_type table   type    possible_keys   key key_len ref rows    Extra
1   SIMPLE  users   ALL PRIMARY NULL    NULL    NULL    52925   Using filesort
1   SIMPLE  enrollment  ref employeeID,number_term  employeeID  9   ezlrn.users.employeeID  2   Using where
4

2 回答 2

0

您需要enrollment包含（至少部分）number、、term和的表上的索引status。您还需要一个employeeID索引employees（如果它还不是主键，它应该是）。

CREATE INDEX idx1 ON enrollment (number, term, status);
CREATE INDEX idx2 ON users (employeeID); // if needed

这将确保 mysqlenrollment首先使用索引在表中查找，然后再加入users表。

于 2012-09-12T19:56:17.573 回答
0

为了详尽地回答，我们需要检查您获得的查询计划，EXPLAIN SELECT...(your query)以及已经存在的索引结构。

在您还没有索引的假设中（可能除了PRIMARY KEY那些），这就是问题所在，让我们看看如何制作一些东西（可能进一步改进）：

SELECT
    `users`.`employeeID` as `username`,
    `users`.`firstName` as `fname`,
    `users`.`lastName` as `lname`
FROM `enrollment`
    INNER JOIN `users` ON `enrollment`.`employeeID` = `users`.`employeeID`
WHERE `enrollment`.`number` = [int]
    AND
    `enrollment`.`term` = [int]
    AND
    (
        `enrollment`.`status` = 'E'
    OR
    `enrollment`.`status` = 'M'
    )
    ORDER BY    
        `users`.`lastName` ASC,
        `users`.`firstName` ASC;

你有一个JOIN从句 between enrollment.employeeIDand users.employeeID。

所以你需要的前几个索引就在那里：

-- CREATE INDEX enrollment_ndx ON enrollment(employeeID); -- wait on this one
CREATE INDEX users_ndx ON users(employeeID);

然后该WHERE子句包含更多可以有用索引的条件。所以最终的索引enrollment是：

CREATE INDEX enrollment_ndx ON enrollment(employeeID, number, term, status);

尝试在注册和用户上创建索引，然后重试（发布查询计划）。

注意：您也可以enrollment.status IN ('M', 'E')在查询中使用语法来简化它。

于 2012-09-12T19:48:27.443 回答