[英]How to count the number of grouped rows in mysql when I already count the total rows
我有下表,我想做以下事项:
计算每个项目在表格中显示的次数
计算DISTINCT
项目数
按名称对项目进行分组
+-------+---------+ | id | names | +-------+---------+ | 1 | Apple | | 2 | Orange | | 3 | Grape | | 4 | Apple | | 5 | Apple | | 6 | Orange | | 7 | Apple | | 8 | Grape | +-------+---------+
对于1.和3.点我有以下查询,它运作得很好:
SELECT * , COUNT(names) as count_name, FROM tbl_products WHERE type = '1' GROUP BY names
所以我得到:
Apple (4) Orange (2) Grape (2)
现在我想计算按行分组的数量并添加一行来计算不同的元素,但是有一些问题,因为MySQL接受查询但不能输出结果:
SELECT * ,
COUNT(names) as count_name,
COUNT(DISTINCT names) as count_total
FROM tbl_products WHERE type = '1'
GROUP BY names
任何人都可以建议可能是什么问题?
编辑:为了更多的清关我想得到这样的表:
+-------+---------+------------+-------------+
| id | names | count_ctg | count_total |
+-------+---------+------------+-------------+
| 1 | Apple | 4 | 3 |
| 2 | Orange | 2 | 3 |
| 3 | Grape | 2 | 3 |
+-------+---------+------------+-------------+
为什么不直接使用您正在使用的查询:
SELECT * ,
COUNT(names) as count_name,
FROM tbl_products WHERE type = '1'
GROUP BY names
该查询实现了所有三个目标。
1)您可以计算count_name
中每个名称值的count_name
。
2)由于您按names
分组,因此不同names
值的数量将等于结果集中的行数。 几乎任何客户端MySQL数据库连接库都可以让您检索此值。
3)您通过明确使用GROUP BY names
满足您按名称分组的第三个标准
当然,结果集中id
的值是没有意义的,您可能只想选择names
和count_names
。
1 - 。计算每个项目在表格中出现的次数:
SELECT names, count(names) FROM tbl_products WHERE type = '1' group by names
2 - 。 表中存在多少个不同的项:
SELECT DISTINCT names FROM tbl_products WHERE type = '1'
3-。 按名称对项目进行分组:
SELECT count(DISTINCT names) as Total FROM tbl_products WHERE type = '1'
作为您的最后一次编辑(ALL IN ONE):
SELECT id, names, count(names), total FROM tbl_products, (select count(distinct names) as total from tbl_products) as total WHERE type = '1' group by names
您可以在子查询中获取不同名称的计数,然后将该东西连接到您已经为1和3求解的主查询中:
SELECT names ,
COUNT(names) as count_name,
Total
FROM tbl_products
OUTER JOIN (SELECT count(DISTINCT names) as Total FROM tbl_products) t2
WHERE type = '1'
GROUP BY names
您可以使用SQL Windowing OVER()
此查询将row_number()函数作为结果中的id列返回,row_number的over(...)需要order by子句。 您可以按照您想要的任何方式订购,但大部分都是按订单排序。
;WITH vwGroups (name, Quantity) AS
(
SELECT name
, COUNT(*)
FROM tbl_products
GROUP BY name
)
SELECT ROW_NUMBER() OVER(ORDER BY Quantity DESC, name) AS id
, name
, Quantity AS count_name
, COUNT(*) OVER () AS count_total
FROM vwGroups
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