Mysql 在自联接查询中使用COUNT_Mysql

Mysql 在自联接查询中使用COUNT

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Mysql 在自联接查询中使用COUNT,mysql,Mysql,我有一个填充双选择列表的查询。该查询通过自联接从同一个表中检索主类别和子类别。基本上，它使用id和父id连接自身以获取每个类别中的子类别。我尝试使用COUNT来获取子类别的数量，以便将该数量添加到第一个列表的输出中。我没有编写查询，我只是想对它进行重构以计算每个main中的sub SELECT root.name AS root_name, root.link AS root_link, root.RETAIL AS root_RETAIL, root.W

我有一个填充双选择列表的查询。该查询通过自联接从同一个表中检索主类别和子类别。基本上，它使用id和父id连接自身以获取每个类别中的子类别。我尝试使用COUNT来获取子类别的数量，以便将该数量添加到第一个列表的输出中。我没有编写查询，我只是想对它进行重构以计算每个main中的sub

SELECT 
    root.name AS root_name, 
    root.link AS root_link, 
    root.RETAIL AS root_RETAIL, 
    root.WHOLESALE AS root_WHOLESALE,
    root.linkto AS root_linkto, 
    root.keywords AS root_keywords, 
    root.description AS root_description, 
    root.id AS root_id,
    down1.name AS down1_name,
    down1.linkto AS down1_linkto, 
    down1.link AS down1_link, 
    down1.keywords AS down1_keywords,
    down1.description AS down1_description, 
    down1.id AS down1_id, 
    down1.parentid AS down1_parentid, 
    down1.RETAIL AS down1_RETAIL, 
    down1.WHOLESALE AS down1_WHOLESALE
FROM categories AS root
        LEFT OUTER JOIN categories AS down1 ON down1.parentid = root.id
WHERE root.parentid = 0
ORDER BY root_name, down1_name

这将返回填充两个列表的所有内容。我尝试将

down1\u name

或

down1\u id

包围在

COUNT

中，但它计算所有内容，而不是每个main中的sub数。我不确定是否要使用另一个自联接来执行此操作，或者使用嵌套的

选择和计数。如有任何见解，将不胜感激。Tks.
如果你尝试这样的东西
select count(cs.down1_name) as mycount from
    (
    SELECT root.name AS root_name, 
    root.link AS root_link, 
    root.RETAIL AS root_RETAIL, 
    root.WHOLESALE AS root_WHOLESALE,
    root.linkto AS root_linkto, 
    root.keywords AS root_keywords, 
    root.description AS root_description, 
    root.id AS root_id,
    down1.name AS down1_name,
    down1.linkto AS down1_linkto, 
    down1.link AS down1_link, 
    down1.keywords AS down1_keywords,
    down1.description AS down1_description, 
    down1.id AS down1_id, 
    down1.parentid AS down1_parentid, 
    down1.RETAIL AS down1_RETAIL, 
    down1.WHOLESALE AS down1_WHOLESALE
    FROM categories AS root
    LEFT OUTER JOIN categories AS down1 ON down1.parentid = root.id
    WHERE root.parentid = 0
    ORDER BY root_name, down1_name ) as cs
    group by cs.down1_name

-----------------更新-------------------------------------
像这样的
SELECT cat_a.name, 
   cat_a.link, 
   cat_a.RETAIL, 
   cat_a.WHOLESALE,
   cat_a.linkto, 
   cat_a.keywords, 
   cat_a.description, 
   cat_a.id,
   cat_b.name cat_b_name,
   cat_b.linkto cat_b_linkto, 
   cat_b.link cat_b_link, 
   cat_b.keywords cat_b_keywords,
   cat_b.description cat_b_description, 
   cat_b.id cat_b_id, 
   cat_b.parentid cat_b_parentid, 
   cat_b.RETAIL cat_b_RETAIL, 
   cat_b.WHOLESALE cat_b_WHOLESALE,
   (SELECT COUNT(1) FROM categories 
     WHERE parentid = cat_a.id) as cat_b_count
FROM categories cat_a LEFT OUTER JOIN categories cat_b 
ON (cat_b.parentid = cat_a.id)
WHERE cat_a.parentid = 0

这是小提琴：
如果你尝试这样的东西
select count(cs.down1_name) as mycount from
    (
    SELECT root.name AS root_name, 
    root.link AS root_link, 
    root.RETAIL AS root_RETAIL, 
    root.WHOLESALE AS root_WHOLESALE,
    root.linkto AS root_linkto, 
    root.keywords AS root_keywords, 
    root.description AS root_description, 
    root.id AS root_id,
    down1.name AS down1_name,
    down1.linkto AS down1_linkto, 
    down1.link AS down1_link, 
    down1.keywords AS down1_keywords,
    down1.description AS down1_description, 
    down1.id AS down1_id, 
    down1.parentid AS down1_parentid, 
    down1.RETAIL AS down1_RETAIL, 
    down1.WHOLESALE AS down1_WHOLESALE
    FROM categories AS root
    LEFT OUTER JOIN categories AS down1 ON down1.parentid = root.id
    WHERE root.parentid = 0
    ORDER BY root_name, down1_name ) as cs
    group by cs.down1_name

-----------------更新-------------------------------------
像这样的
SELECT cat_a.name, 
   cat_a.link, 
   cat_a.RETAIL, 
   cat_a.WHOLESALE,
   cat_a.linkto, 
   cat_a.keywords, 
   cat_a.description, 
   cat_a.id,
   cat_b.name cat_b_name,
   cat_b.linkto cat_b_linkto, 
   cat_b.link cat_b_link, 
   cat_b.keywords cat_b_keywords,
   cat_b.description cat_b_description, 
   cat_b.id cat_b_id, 
   cat_b.parentid cat_b_parentid, 
   cat_b.RETAIL cat_b_RETAIL, 
   cat_b.WHOLESALE cat_b_WHOLESALE,
   (SELECT COUNT(1) FROM categories 
     WHERE parentid = cat_a.id) as cat_b_count
FROM categories cat_a LEFT OUTER JOIN categories cat_b 
ON (cat_b.parentid = cat_a.id)
WHERE cat_a.parentid = 0

这里是关键：
尝试使用子查询
SELECT r.name AS r_name, 
       r.link AS r_link, 
       r.RETAIL AS r_RETAIL, 
       r.WHOLESALE AS r_WHOLESALE,
       r.linkto AS r_linkto, 
       r.keywords AS r_keywords, 
       r.description AS r_description, 
       r.id AS r_id,
       d.name AS d_name,
       d.linkto AS d_linkto, 
       d.link AS d_link, 
       d.keywords AS d_keywords,
       d.description AS d_description, 
       d.id AS d_id, 
       d.parentid AS d_parentid, 
       d.RETAIL AS d_RETAIL, 
       d.WHOLESALE AS d_WHOLESALE,
       (SELECT COUNT(*) FROM categories 
         WHERE parentid = r.id) d_count
  FROM categories AS r LEFT OUTER JOIN categories AS d 
    ON d.parentid = r.id
 WHERE r.parentid = 0
 ORDER BY r_name, d_name

尝试使用子查询
SELECT r.name AS r_name, 
       r.link AS r_link, 
       r.RETAIL AS r_RETAIL, 
       r.WHOLESALE AS r_WHOLESALE,
       r.linkto AS r_linkto, 
       r.keywords AS r_keywords, 
       r.description AS r_description, 
       r.id AS r_id,
       d.name AS d_name,
       d.linkto AS d_linkto, 
       d.link AS d_link, 
       d.keywords AS d_keywords,
       d.description AS d_description, 
       d.id AS d_id, 
       d.parentid AS d_parentid, 
       d.RETAIL AS d_RETAIL, 
       d.WHOLESALE AS d_WHOLESALE,
       (SELECT COUNT(*) FROM categories 
         WHERE parentid = r.id) d_count
  FROM categories AS r LEFT OUTER JOIN categories AS d 
    ON d.parentid = r.id
 WHERE r.parentid = 0
 ORDER BY r_name, d_name

通过查询，这可能会更容易。类似这样（我们假设主查询名为q1）

选择r\u id maincat
，计数（*）子类别
从第一季度开始
其中d_name不为空
按r\u id分组
选择q1*
，子类别
从第一季度到第二季度
其中r_id=maincat

然后使用q3而不是q1来填充列表。
这可能更容易查询查询。类似这样（我们假设主查询名为q1）

选择r\u id maincat
，计数（*）子类别
从第一季度开始
其中d_name不为空
按r\u id分组
选择q1*
，子类别
从第一季度到第二季度
其中r_id=maincat

然后用q3而不是q1填充列表。
我想你误解了这个问题。他还需要返回其他列，而不仅仅是一个计数
。他可以以单独的方式执行这两个查询，或者调整这一个以填充他的查询。上面的查询返回一个计数，而他正在查找每个父项的计数，如@peterm的示例中所示。一个计数……您是否通过cs.down1\u name看到这个组，在问题的结尾？？不，我完全没有注意到。我还没有测试过它，但我非常确定按cs.down1\u name
分组仍然不会返回正确的计数。。。（见原问题）。你测试过了吗？我想你误解了这个问题。他还需要返回其他列，而不仅仅是一个计数
。他可以以单独的方式执行这两个查询，或者调整这一个以填充他的查询。上面的查询返回一个计数，而他正在查找每个父项的计数，如@peterm的示例中所示。一个计数……您是否通过cs.down1\u name看到这个组，在问题的结尾？？不，我完全没有注意到。我还没有测试过它，但我非常确定按cs.down1\u name
分组仍然不会返回正确的计数。。。（见原问题）。您测试过吗？这将返回一个语法错误，试图对其进行排序。我试过类似的东西，结果都一样。Tks@史蒂夫：对不起，这只是d.wholesal后面省略了一个逗号，作为d\u wholesal，
。请参阅更新的答案，啊，我放了一个，但也用作d_计数的前面。很好！非常感谢！此外，在这篇文章之前，我自己尝试过这一点，我在我的别名中使用了嵌套SELECT，其中您的别名是d_count。没有意识到我不需要它。@Steve非常欢迎：）因为
是可选的。为了保证查询的一致性，您可以在d_count之前使用它。这将返回一个语法错误，并尝试对其进行排序。我试过类似的东西，结果都一样。Tks@史蒂夫：对不起，这只是d.wholesal后面省略了一个逗号，作为d\u wholesal，
。请参阅更新的答案，啊，我放了一个，但也用作d_计数的前面。很好！非常感谢！此外，在这篇文章之前，我自己尝试过这一点，我在我的别名中使用了嵌套SELECT，其中您的别名是d_count。没有意识到我不需要它。@Steve非常欢迎：）因为
是可选的。为了在查询中保持一致性，您可以在d_count之前使用它。我考虑在CF代码中使用此方法，因为它很好且经过封装，如果我可以获得正确的计数，只需为其创建一个变量并以这种方式输出即可。还没什么，但我在查询原始查询。tks！我考虑在CF代码中使用这个方法，因为它很好，而且是封装的，如果我能得到正确的计数，只需为它创建一个变量并以这种方式输出即可。还没什么，但我在查询原始查询。tks！