Question

我对编码很陌生，并且出于我自己的兴趣，我正在尝试创建一个工作的数据库系统，并且随着我的进展而非常学习。

我有一个数据库查询，旨在显示Sample Name，Tank Name和Customer匹配的最近结果。这些来自三个不同但相关的表格。

我提出了以下查询。 此查询工作但是对于我自己的教育，我是在正确的方向上工作还是有更好的方法来解决这个问题（这看起来非常不整洁，难以读懂我的想法）？

SELECT 
  `t_workorders`.`Work Order`,
  `t_workorders`.`Date Sampled`,
  `Result`,
  `t_test_units`.`Unit` 
FROM
  `t_sampletests` 
  RIGHT JOIN `t_samples` 
    ON `Sample` = `pk_Sample` 
  RIGHT JOIN `t_workorders` 
    ON `t_samples`.`Work Order` = `t_workorders`.`Work Order` 
  LEFT JOIN `t_test_units` 
    ON `t_sampletests`.`Unit` = `t_test_units`.`pk_Unit` 
WHERE `t_sampletests`.`Test` = 
  (SELECT 
    `Test` 
  FROM
    `t_sampletests` 
  WHERE `pk_SampleTest` = $ testID) 
  AND `t_Samples`.`Sample Name` = 
  (SELECT 
    `Sample Name` 
  FROM
    `t_sampletests` 
    LEFT JOIN `t_Samples` 
      ON `Sample` = `pk_Sample` 
  WHERE `pk_SampleTest` = $ testID) 
  AND `t_Samples`.`Tank` = 
  (SELECT 
    `Tank` 
  FROM
    `t_sampletests` 
    LEFT JOIN `t_Samples` 
      ON `Sample` = `pk_Sample` 
  WHERE `pk_SampleTest` = $ testID) 
  AND `t_workorders`.`Customer` = 
  (SELECT 
    `Customer` 
  FROM
    `t_sampletests` 
    LEFT JOIN `t_Samples` 
      ON `Sample` = `pk_Sample` 
    LEFT JOIN `t_workorders` 
      ON `t_Samples`.`Work Order` = `t_workorders`.`Work Order` 
  WHERE `pk_SampleTest` = $ testID) 
  AND `t_workorders`.`Work Order` <> 
  (SELECT 
    `t_workorders`.`Work Order` 
  FROM
    `t_sampletests` 
    LEFT JOIN `t_Samples` 
      ON `Sample` = `pk_Sample` 
    LEFT JOIN `t_workorders` 
      ON `t_Samples`.`Work Order` = `t_workorders`.`Work Order` 
  WHERE `pk_SampleTest` = $ testID) 
ORDER BY `t_workorders`.`Work Order` DESC 
LIMIT 15

非常感谢任何替代或更合适的方法的建议。

非常感谢

Answer 1

这样的事情：

select feild1, field2 from
(select feild1, field2 from table1)as a

left join

select field1, desc from table2) as b
on a.field1 = b.field1

这将优化您的查询

避免选择您未使用它的表格中的所有字段。仅选择要显示为优化的字段

Answer 2

IMO，使用新行和增量将帮助您阅读和构建查询，并让您快速了解它的作用。

我还尝试在使用SQL关键字时保持一致，并以大写形式写出来。

SELECT `t_workorders`.`Work Order`, `t_workorders`.`Date Sampled`, `Result`,`t_test_units`.`Unit`
FROM `t_sampletests`
RIGHT JOIN `t_samples` ON `Sample` = `pk_Sample` 
RIGHT JOIN `t_workorders` ON `t_samples`.`Work Order` = `t_workorders`.`Work Order`
LEFT JOIN `t_test_units`ON `t_sampletests`.`Unit` = `t_test_units`.`pk_Unit`
WHERE `t_sampletests`.`Test` = (
    SELECT `Test` FROM `t_sampletests` WHERE `pk_SampleTest` = $testID
  )
  AND `t_Samples`.`Sample Name` = (
    SELECT `Sample Name`
    FROM `t_sampletests`
    LEFT JOIN `t_Samples` ON `Sample` = `pk_Sample` WHERE `pk_SampleTest` = $testID
  )
  AND `t_Samples`.`Tank` = (
    SELECT `Tank`
    FROM `t_sampletests`
    LEFT JOIN `t_Samples` ON `Sample` = `pk_Sample` WHERE `pk_SampleTest` = $testID
  )
  AND `t_workorders`.`Customer`= (
    SELECT `Customer`
    FROM `t_sampletests`
    LEFT JOIN `t_Samples` ON `Sample` = `pk_Sample`
    LEFT JOIN `t_workorders` ON `t_Samples`.`Work Order` = `t_workorders`.`Work Order`
    WHERE `pk_SampleTest` = $testID
  )
  AND `t_workorders`.`Work Order` <> (
    SELECT `t_workorders`.`Work Order`
    FROM `t_sampletests`
    LEFT JOIN `t_Samples` ON `Sample` = `pk_Sample`
    LEFT JOIN `t_workorders` ON `t_Samples`.`Work Order` = `t_workorders`.`Work Order` 
    WHERE `pk_SampleTest` = $testID
  )
ORDER BY `t_workorders`.`Work Order`
DESC LIMIT 15;

（并且不要忘记查询后面的;）

Mysql查询代码改进

2 个答案: