Question

我使用jdbc运行此查询并成功在MySQL中获得结果：

SELECT COUNT(DISTINCT xx.x, xx.z) as `n_x|z`, 
       COUNT(DISTINCT xx.w, xx.y, xx.z) as `n_w|y|z` /*,...same COUNTS*/
       FROM (SELECT x0.field0 as `x`, x0.field1 as `y`, x0.field2 as `z`, 
       x0.field3 as `w` FROM `Kind` x0 ) as xx

以下查询也成功生成结果：

SELECT (1  * -1.5) as weight,
       xx.x, xx.y, xx.z, xx.w
/*The same table:*/
       FROM (SELECT x0.field0 as `x`, x0.field1 as `y`, x0.field2 as `z`, 
       x0.field3 as `w` FROM `Kind` x0 ) as xx

但是组合：

SELECT COUNT(DISTINCT xx.x, xx.z) as `n_x|z`, 
       COUNT(DISTINCT xx.w, xx.y, xx.z) as `n_w|y|z` /*,... same COUNTs*/
       ,(1  * -1.5) as weight,
       xx.x, xx.y, xx.z, xx.w
/*The same table:*/
       FROM (SELECT x0.field0 as `x`, x0.field1 as `y`, x0.field2 as `z`, 
       x0.field3 as `w` FROM `Kind` x0 ) as xx

犯了错误：

您的SQL语法有错误;检查手册对应于您的MySQL服务器版本，以便使用正确的语法靠近＆＃39; xx.x，xx.y，xx.z，xx.w FROM（SELECT x0.field0 as x，x0.field1 如y，x0.fie＆＃39;在第1行

即使删除,(1 * -1.5) as weight也无济于事！我可以单独运行两个查询，但我更喜欢将它们组合起来，以便从复杂耗时的查询中获取表：

FROM (SELECT x0.field0 as `x`, x0.field1 as `y`, x0.field2 as `z`, x0.field3 as `w` FROM `Kind` x0 ) as xx"

生成一次。我做错了什么？

Answer 1

小心你在第一个查询中有一个关于行总数的聚合

在第二个中你有没有任何聚合的行

您从两个查询中选择不同数量的行所以你应该为非聚合函数或者分组，例如：

SELECT COUNT(DISTINCT xx.x, xx.z) as `n_x|z`, 
       COUNT(DISTINCT xx.w, xx.y, xx.z) as `n_w|y|z`
       ,(1  * -1.5) as weight,
       xx.x, xx.y, xx.z, xx.w

       FROM (SELECT x0.field0 as `x`, x0.field1 as `y`, x0.field2 as `z`, 
       x0.field3 as `w` FROM `Kind` x0 ) as xx 
       group by  weight, xx.x, xx.y, xx.z, xx.w

或（取决于您的应用程序需求）在不平行的行上使用聚合函数（例如：min（））

SELECT COUNT(DISTINCT xx.x, xx.z) as `n_x|z`, 
       COUNT(DISTINCT xx.w, xx.y, xx.z) as `n_w|y|z`,
       min((1  * -1.5)) as weight,
       min(xx.x), 
       min(xx.y), 
       min(xx.z), 
       min(xx.w)

       FROM (SELECT x0.field0 as `x`, x0.field1 as `y`, x0.field2 as `z`, 
       x0.field3 as `w` FROM `Kind` x0 ) as xx 
       group by  weight, xx.x, xx.y, xx.z, xx.w

或者如同您在上次评论中一样，如果您希望重复计算xx中的所有行，您可以使用CROSS JOIN

  SELECT c_xx.`n_x|z`, c_xx.`n_w|y|z`, 
         (1  * -1.5) as weight,
         xx1.x, xx1.y, xx1.z, xx1.w
  FROM (SELECT x0.field0 as `x`, x0.field1 as `y`, x0.field2 as `z`, 
         x0.field3 as `w` FROM `Kind` x0 ) xx1 

  CROSS JOIN (

      SELECT COUNT(DISTINCT xx.x, xx.z) as `n_x|z`, 
             COUNT(DISTINCT xx.w, xx.y, xx.z) as `n_w|y|z` //,... same COUNTS
             FROM (SELECT x0.field0 as `x`, x0.field1 as `y`, x0.field2 as `z`, 
             x0.field3 as `w` FROM `Kind` x0 ) xx
  ) c_xx

与其他查询一起使用count时出现MySQL错误

1 个答案: