Question

我有这个MSSQL查询工作

SELECT c.CategoryName + ' (' + cast(count(ic.CategoryId) as varchar(255)) + ')' AS
 CategoryName, count(ic.CategoryId) AS NumPhotos,
  c.Slug, c.ParentCategoryId, c.Id
FROM Categories
 c LEFT JOIN
 ItemCategories ic
 on ic.CategoryId = c.Id
GROUP BY c.CategoryName, c.slug, c.ParentCategoryId, c.id
ORDER BY ParentCategoryId DESC

我想只返回行，WHERE NumPhotos＆gt; 0但SQL WHERE子句不允许使用临时列

Answer 1

having子句是您问题的规范解决方案。但是，我怀疑inner join也是合适的：

SELECT c.CategoryName + ' (' + cast(count(ic.CategoryId) as varchar(255)) + ')' AS CategoryName,
       count(ic.CategoryId) AS NumPhotos,
       c.Slug, c.ParentCategoryId, c.Id
FROM Categories c INNER JOIN
     ItemCategories ic
     on ic.CategoryId = c.Id
GROUP BY c.CategoryName, c.slug, c.ParentCategoryId, c.id
ORDER BY ParentCategoryId DESC;

没有样本数据，很难确定，但我很确定这会做同样的事情。

inner join的优势在于它可能更有效，因为处理的数据更少（可能只是略少），优化器有更多机会选择最佳join算法。 / p>

Answer 2

现有评论给出了足够的答案，但这是另一种解决方案，使用＆＃34;虚拟表＆＃34;：

SELECT * FROM ( 
SELECT c.CategoryName + ' (' + cast(count(ic.CategoryId) as varchar(255)) + ')' AS
 CategoryName, count(ic.CategoryId) AS NumPhotos,
  c.Slug, c.ParentCategoryId, c.Id
FROM Categories
 c LEFT JOIN
 ItemCategories ic
 on ic.CategoryId = c.Id
GROUP BY c.CategoryName, c.slug, c.ParentCategoryId, c.id
) 
WHERE NumPhotos>0
ORDER BY ParentCategoryId DESC

SQL WHERE临时列

2 个答案: