复制SQL语句的语法是什么？

Question

我是SQL的新手，我想看看是否有人可以帮助我复制基本SQL百分位语句的语法。这是我想要复制的代码：

SELECT Max(CompData.Salary) AS 50th
FROM (SELECT TOP 50 PERCENT Salary FROM CompData ORDER BY Salary)  AS [%$##@_Alias];

我试过这个：

SELECT Max(CompData.Salary) AS 50th
FROM (SELECT TOP 50 PERCENT Salary FROM CompData ORDER BY Salary)  AS [%$##@_Alias],
FROM (SELECT TOP 60 PERCENT Salary FROM CompData ORDER BY Salary)  AS [%$##@_Alias];

我得到了Syntax错误FROM子句 例如，如何为第60百分位复制此（没有语法错误）？

非常感谢！

Answer 1

您的问题是第二个from。 SQL SELECT只有一个FROM子句（其他from子句将在子查询中。）

你不想要做你正在尝试的事情。问题是,做笛卡尔积。因此，如果您的表有1,000行，那么您的中间结果将具有500 * 600 = 300,000行 - 并且性能受到很大影响。

您可以使用percentile_disc()或precentile_cont()来实现此目的。但是，对于您的查询，您只想在加入之前进行聚合：

SELECT q50.val, q60.val
FROM (SELECT Max(CompData.Salary) AS val
      FROM (SELECT TOP 50 PERCENT Salary FROM CompData ORDER BY Salary) t
     ) q50 CROSS JOIN
     (SELECT Max(CompData.Salary) AS val
      FROM (SELECT TOP 50 PERCENT Salary FROM CompData ORDER BY Salary) t
     ) q60;

还有其他方法可以进行此计算，但这似乎就是您在问题中使用的方法。

编辑：

您的问题被标记为 SQL SERVER 而不是 MS ACCESS 。标签很重要。 MS Access语法更像是：

SELECT q50.val, q60.val
FROM (SELECT Max(CompData.Salary) AS val
      FROM (SELECT TOP 50 PERCENT Salary FROM CompData ORDER BY Salary) as t
     ) as q50,
     (SELECT Max(CompData.Salary) AS val
      FROM (SELECT TOP 50 PERCENT Salary FROM CompData ORDER BY Salary) as t
     ) as q60;