row_number() 总是 return 1 因为源 table 只有一行

Question

让我们考虑这个最小的例子：

SELECT row_number() over() as GID, 
       unnest(myarray)     as letter
FROM 
(
    SELECT string_to_array('a,b,b', ',') as myarray
) AS T

现在由于 table T 只包含一个元素，row_number() 函数总是 return 1 即使 3 行是 return编辑。

所以我得到：

GID   letter
1     "a"
1     "b"
1     "b"

而不是

GID   letter
1     "a"
2     "b"
3     "b"

如何解决？

Answer 1

将 unnest 子句放在 string_to_array 调用周围，这样 T 已经有多个行：

SELECT row_number() over() as GID, myarray as letter
FROM (
    SELECT unnest(string_to_array('a,b,c', ',')) as myarray
) AS T

此外，我建议使用 WITH ORDINALITY 而不是 row_number() 来获取索引数组元素：

SELECT gid, letter
FROM UNNEST(string_to_array('a,b,c', ',')) WITH ORDINALITY AS T(gid, letter)

如果您想保留返回数组的 select 表达式，这也适用

SELECT gid, letter
FROM UNNEST(
  (SELECT string_to_array('a,b,c', ',') as myarray)
) WITH ORDINALITY AS T(letter, gid)

或使用横向查询：

SELECT gid, letter
FROM
  (SELECT string_to_array('a,b,c', ',') as myarray) AS T,
  UNNEST(T.myarray) WITH ORDINALITY AS U(letter, gid)

Answer 2

按照编辑前的示例，尝试以下查询：

SELECT 
 row_number() OVER () AS gid, ST_AsText(geom)
FROM (SELECT 
        st_makepixel(
          ST_GeomFromText('POLYGON((2580000 1182000,2581000 1182000,2581000 1183000,2580000 1183000,2580000 1182000))',2056),200.0,50) AS geom) j

 gid |                                         st_astext                                          
-----+--------------------------------------------------------------------------------------------
   1 | POLYGON((2580000 1182000,2580200 1182000,2580200 1182200,2580000 1182200,2580000 1182000))
   2 | POLYGON((2580200 1182000,2580400 1182000,2580400 1182200,2580200 1182200,2580200 1182000))
   3 | POLYGON((2580400 1182000,2580600 1182000,2580600 1182200,2580400 1182200,2580400 1182000))
   4 | POLYGON((2580600 1182000,2580800 1182000,2580800 1182200,2580600 1182200,2580600 1182000))
   5 | POLYGON((2580800 1182000,2581000 1182000,2581000 1182200,2580800 1182200,2580800 1182000))
   6 | POLYGON((2580000 1182200,2580200 1182200,2580200 1182400,2580000 1182400,2580000 1182200))
   7 | POLYGON((2580200 1182200,2580400 1182200,2580400 1182400,2580200 1182400,2580200 1182200))
   8 | POLYGON((2580400 1182200,2580600 1182200,2580600 1182400,2580400 1182400,2580400 1182200))
   9 | POLYGON((2580600 1182200,2580800 1182200,2580800 1182400,2580600 1182400,2580600 1182200))
  10 | POLYGON((2580800 1182200,2581000 1182200,2581000 1182400,2580800 1182400,2580800 1182200))
  11 | POLYGON((2580000 1182400,2580200 1182400,2580200 1182600,2580000 1182600,2580000 1182400))
  12 | POLYGON((2580200 1182400,2580400 1182400,2580400 1182600,2580200 1182600,2580200 1182400))
  13 | POLYGON((2580400 1182400,2580600 1182400,2580600 1182600,2580400 1182600,2580400 1182400))
  14 | POLYGON((2580600 1182400,2580800 1182400,2580800 1182600,2580600 1182600,2580600 1182400))
  15 | POLYGON((2580800 1182400,2581000 1182400,2581000 1182600,2580800 1182600,2580800 1182400))
  16 | POLYGON((2580000 1182600,2580200 1182600,2580200 1182800,2580000 1182800,2580000 1182600))
  17 | POLYGON((2580200 1182600,2580400 1182600,2580400 1182800,2580200 1182800,2580200 1182600))
  18 | POLYGON((2580400 1182600,2580600 1182600,2580600 1182800,2580400 1182800,2580400 1182600))
  19 | POLYGON((2580600 1182600,2580800 1182600,2580800 1182800,2580600 1182800,2580600 1182600))
  20 | POLYGON((2580800 1182600,2581000 1182600,2581000 1182800,2580800 1182800,2580800 1182600))
  21 | POLYGON((2580000 1182800,2580200 1182800,2580200 1183000,2580000 1183000,2580000 1182800))
  22 | POLYGON((2580200 1182800,2580400 1182800,2580400 1183000,2580200 1183000,2580200 1182800))
  23 | POLYGON((2580400 1182800,2580600 1182800,2580600 1183000,2580400 1183000,2580400 1182800))
  24 | POLYGON((2580600 1182800,2580800 1182800,2580800 1183000,2580600 1183000,2580600 1182800))
  25 | POLYGON((2580800 1182800,2581000 1182800,2581000 1183000,2580800 1183000,2580800 1182800))
(25 Zeilen)

row_number() 总是 return 1 因为源 table 只有一行

row_number() always return 1 since the source table has only one row

postgresql

postgis

row-number