Question

假设我有下表：

first  second
A      1
A      1
A      2
B      1
B      2
C      1
C      1

如果我运行以下查询：

select first, second, count(second) from tbl group by first, second

它将生成一个包含以下信息的表：

first  second  count(second)
A      1       2
A      2       1
B      1       1
B      2       1
C      1       2

如何编写查询，以便我从第二列的选项中获取信息作为列，这些列的值是这样的计数：

first  1  2
A      2  1
B      1  1
C      2  0

Answer 1

您可以使用CASE：

SELECT  "first",
        SUM(CASE WHEN "second" = 1 THEN 1 ELSE 0 END) AS "1",
        SUM(CASE WHEN "second" = 2 THEN 1 ELSE 0 END) AS "2"
FROM tbl
GROUP BY "first"

格式化查询结果

1 个答案: