SQL SQL查找列中每种类型的总数
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SQL find total count of each type in a column
提问by Wes Doyle
I'm learning SQL and am stumped on what should be a simple query. I have a table with the following pattern:
我正在学习 SQL 并且对什么应该是一个简单的查询感到困惑。我有一个具有以下模式的表：
Id | Type
------------
1 | Red
2 | Blue
3 | Blue
4 | Red
..
I would like to write a query to return a table that counts the total number of instances of each type and returns a table with the following pattern, for example, if 'Blue' occurs in 12 rows, and 'Red' occurs in 16 rows in the table above, the result would be:
我想编写一个查询来返回一个表，该表计算每种类型的实例总数并返回一个具有以下模式的表，例如，如果 'Blue' 出现在 12 行中，而 'Red' 出现在 16 行中在上表中，结果将是：
Blue | Red
-----------
12 | 16
回答by Will
You could do it this way:
你可以这样做：
SELECT Type, COUNT(*) FROM TABLE GROUP BY Type
If you'd like to see the Types in separate columns, you could do this:
如果您想在单独的列中查看类型，您可以这样做：
SELECT SUM(CASE WHEN Type = 'Blue' THEN 1 ELSE 0 END) AS Blue, SUM(CASE WHEN Type = 'Red' THEN 1 ELSE 0 END) AS Red FROM TABLE
