PostgreSQL：存储过程从几个有条件的行中返回一个假行

Question

考虑下表：

Value1 Value2 Value3
1      1      0.9
1      2      0.8
1      3      0.1
2      1      0.1
2      2      0.15

我只需要返回符合以下条件的行： 考虑按 Value1 分组：

1. 从每个组中返回 Value3 >= 0.8 的所有行。
2. 如果组中所有行的 Value3

对于提到的表格，结果将是：

Value1 Value2 Value3
1      1      0.9
1      2      0.8
2      0      0.15

这种逻辑在 PostgreSQL 中是如何实现的（例如使用存储过程）？

提前致谢。

Answer 1

使用union:

select *
from a_table
where value3 >= 0.8

union all

select value1, 0, max(value3)
from a_table
group by value1
having max(value3) <= 0.2;

根据查询创建sql函数很容易，例如：

create or replace function select_from_a_table(limit1 numeric, limit2 numeric)
returns setof a_table language sql as $$
    select *
    from a_table
    where value3 >= limit1
    union all
    select value1, 0, max(value3)
    from a_table
    group by value1
    having max(value3) <= limit2;
$$;

select * from select_from_a_table(0.8, 0.2);

 value1 | value2 | value3 
--------+--------+--------
      1 |      1 |    0.9
      1 |      2 |    0.8
      2 |      0 |   0.15
(3 rows)

Answer 2

试试这个

SELECT a.Value1,
       Value2,
       Value3
FROM   Yourtable a
       JOIN (SELECT Value1
             FROM   Yourtable 
             GROUP  BY Value1
             HAVING Count(CASE
                            WHEN Value3 >= 0.8 THEN 1
                          END) >= 1) b
         ON a.Value1 = b.Value1
Where Value3 >= 0.8 
UNION ALL
SELECT Value1,
       0             AS Value2,
       Max(Value3) AS Value3
FROM   Yourtable a
WHERE  NOT EXISTS (SELECT Value1
                   FROM   Yourtable b
                   WHERE  a.Value1 = b.Value1
                   GROUP  BY Value1
                   HAVING Count(CASE
                                  WHEN Value3 >= 0.8 THEN 1
                                END) >= 1) 
group by Value1

• SQL FIDDLE DEMO

Answer 3

可以用一个聚合来做你想做的事：

select value1,
       (case when max(value3) < 0.8 then 0 else max(value2) end) as value2,
       max(value3) as value3
from t
group by value1,
         (case when value3 >= 0.8 then value2 end),
         (case when value3 >= 0.8 then value3 end)
having max(value3) over (partition by value1) < 0.8 or
       max(value3) >= 0.8;

这确实假设value2 和value3 是唯一的。