格式化查询结果

Question

比方说，我有如下表：

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

如果我运行下面的查询：

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

它会产生以下信息表：

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

我该如何编写查询，以便使用第二列中的选项给出信息对于这些列是这样的数列和值：

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"