如何在数组上进行相等测试

Question

我正在尝试聚合ID上的值。如果它们都相同，我会返回它们，但如果遇到这两个值，则必须创建另一个值“C”。

CREATE TABLE foo (
    fooid int,
    foocomm text
); 

INSERT INTO foo (fooid,foocomm)
VALUES (1,'A'); 
INSERT INTO foo (fooid,foocomm)
VALUES (1,'B'); 
INSERT INTO foo (fooid,foocomm)
VALUES (2,'A');

SELECT 
  CASE 

    WHEN array_remove(array_agg(foocomm),NULL) = {'A'} THEN 'A'
    WHEN array_remove(array_agg(foocomm),NULL) = {'B'} THEN 'B'
    WHEN array_remove(array_agg(foocomm),NULL) = {'A','B'} THEN 'C'
  END AS BAR

FROM foo
GROUP BY fooid;

它应该屈服

fooid,foocomm
1, 'C'
2, 'A'

Answer 1

t=# SELECT fooid,
  CASE
    WHEN array_remove(array_agg(foocomm order by foocomm),NULL) = '{A}' THEN 'A'
    WHEN array_remove(array_agg(foocomm order by foocomm),NULL) = '{B}' THEN 'B'
    WHEN array_remove(array_agg(foocomm order by foocomm),NULL) = '{A,B}' THEN 'C'
  END AS BAR
FROM foo
GROUP BY fooid;
 fooid | bar
-------+-----
     1 | C
     2 | A
(2 rows)

您的查询有效，只需修复数组文本表示：

https://www.postgresql.org/docs/current/static/arrays.html#ARRAYS-INPUT