Question

我正在尝试研究是否可以在SQL中进行以下转换：

+--------+--------+--------+
|POLICY_1|POLICY_2|POLICY_3|
+--------+--------+--------+
|T       |T       |F       |
+--------+--------+--------+
|F       |T       |F       |
+--------+--------+--------+
|T       |T       |T       |
+--------+--------+--------+

是否可以查询此表并最终得到如下所示的结果集：

+------+-----+
|POLICY|COUNT|
+------+-----+
|1     |2    |
+------+-----+
|2     |3    |
+------+-----+
|3     |1    |
+------+-----+

我想知道一般的SQL术语，但是重要的是我正在使用Postgres（9.2）

Answer 1

Union All，Aggregate和CASE Version

 select 1 as POLICY, SUM(case when POLICY_1 = 'T' THEN 1 ELSE 0 end) as COUNT
  from POLICIES
  union all
 select 2 as POLICY, SUM(case when POLICY_2 = 'T' THEN 1 ELSE 0 end) as COUNT
  from POLICIES
  union all
 select 3 as POLICY, SUM(case when POLICY_3 = 'T' THEN 1 ELSE 0 end) as COUNT
  from POLICIES

* Unpivot版本：* （MicroSoft T-SQL特定）

如果您坚持要将行转换为列，则可以使用PIVOT / UNPIVOT功能。

SELECT ROW_NUMBER() OVER (ORDER BY PolicyName) AS Row, * 
 FROM ( select SUM(CASE WHEN Policy_1 = 'T' THEN 1 ELSE 0 END) as Policy_1,
               SUM(CASE WHEN Policy_2 = 'T' THEN 1 ELSE 0 END) as Policy_2,
               SUM(CASE WHEN Policy_3 = 'T' THEN 1 ELSE 0 END) as Policy_3
        from POLICIES
      )p
 UNPIVOT ( T_Count FOR PolicyName  in ([Policy_1], [Policy_2], [Policy_3]))unpvt

Unnest版本（postgre sql特定）
所有学分转到 Francis ，主题播放者，我只是在这里发布。

select
    UNNEST((select array_agg(generate_series) 
            from generate_series(1,3))) as policy_name,
    UNNEST(array[
             sum(case when policy_1 = 't' then 1 else 0 end),
             sum(case when policy_2 = 't' then 1 else 0 end),
             sum(case when policy_3 = 't' then 1 else 0 end)
           ]) as count from POLICY

Answer 2

根据建议，这是Postgresql的UNNEST版本：

select
    UNNEST((select array_agg(generate_series) from generate_series(1,3))) as policy_name,
    UNNEST(array[
        sum(case when policy_1 = 't' then 1 else 0 end),
        sum(case when policy_2 = 't' then 1 else 0 end),
        sum(case when policy_3 = 't' then 1 else 0 end)
    ]) as count from POLICY

sql将行的布尔行合并为行

2 个答案: