Question

这是我的疑问：

SELECT A.term_id, 
       B.name, 
       counts
FROM wp_term_taxonomy A
LEFT JOIN (
SELECT COUNT( C.parent ) AS counts
FROM wp_term_taxonomy C
GROUP BY C.term_id
) AS T ON A.term_id = T.parent -- This line causes error
JOIN wp_terms B ON A.term_id = B.term_id
WHERE A.taxonomy =  'product_cat'
AND A.parent =0

运行此语法时出现此错误：

＃1054 - 'on clause'
中的未知列'T.parent'

如何使用ON？

正确引用我的子查询选择语句

Answer 1

您不能使用on子句为不存在的列加入表格（在您没有在dinamically生成的表格T中选择的情况下）

您应该在t表中添加父列，例如：

SELECT A.term_id, B.name, counts
FROM wp_term_taxonomy A
LEFT JOIN (
  SELECT C.term_id as parent, COUNT( C.parent ) AS counts
  FROM wp_term_taxonomy C
  GROUP BY C.term_id
) AS T ON A.term_id = T.parent /* This line causes error*/
JOIN wp_terms B ON A.term_id = B.term_id
WHERE A.taxonomy =  'product_cat'
AND A.parent =0

MySql JOINS和Count（）函数：＃1054 - 'on子句'中的未知列'T.parent'

1 个答案: