mysql计算

Question

这是我的查询

SELECT
  pa.products_attributes_id,
  pa.products_id,
  pa.options_id
FROM products_attributes pa
LEFT JOIN products_description pd
  ON pa.products_id = pd.products_id
  AND pd.language_id = '1'
LEFT JOIN products_attributes_groups pag
  ON pa.products_attributes_id = pag.products_attributes_id
WHERE pa.products_id = '109'
GROUP BY pa.products_attributes_id
ORDER BY pa.attribute_sort

正如您在上一栏options_id中所见，有3个唯一的选项ID（即2,13和1）

我想要实现的是计算option_id列中唯一ID的数量。在上面的结果集中，查询应该返回3（因为有3个唯一的option_ids 2,13和1）。 如果此计数出现在包含结果集所有行的新temprary列中，我就不会有问题

P.S：我不想在获取数据时需要更改GROUP BY pa.products_attributes_id

编辑：使用(SELECT COUNT(DISTINCT options_id) FROM products_attributes ) AS options_id_count结果集现在是12，这是错误的（它应该是3）

Answer 1

您可以使用COUNT(DISTINCT options_id) as field_name：）

Answer 2

假设<REST_OF_YOUR_QUERY>是以LEFT JOIN

开头的查询的一部分

SELECT
  pa.products_attributes_id,
  pa.products_id,
  pa.options_id,
  (
     SELECT COUNT(DISTINCT options_id) 
     FROM products_attributes
     <REST_OF_YOUR_QUERY>
  ) option_count
FROM products_attributes pa
<REST_OF_YOUR_QUERY>

Answer 3

  

查询应该返回3

这只是options_id products_attributes中products_id的明显统计数字109：

select count(distinct options_id)
from products_attributes 
where products_id = 109;

Answer 4

由于您必须对数据进行两次传递（一次提取结果，一次计算不同的option_id值），您可以将查询放入with中，然后只引用两次。 Oracle会将其优化为临时GTT，并且只读取一次源数据。

WITH d AS
 (SELECT pa.products_attributes_id,
         pa.products_id,
         pa.options_id
    FROM products_attributes pa
    LEFT JOIN products_description pd
      ON pa.products_id = pd.products_id
     AND pd.language_id = '1'
    LEFT JOIN products_attributes_groups pag
      ON pa.products_attributes_id = pag.products_attributes_id
   WHERE pa.products_id = '109'
   GROUP BY pa.products_attributes_id
   ORDER BY pa.attribute_sort)
SELECT d.*,
       (SELECT COUNT(DISTINCT d.options_id)
          FROM d)
  FROM d;