108

当我有一个带有分隔值的列时,我可以使用该unnest()函数:

myTable
id | elements
---+------------
1  |ab,cd,efg,hi
2  |jk,lm,no,pq
3  |rstuv,wxyz

select id, unnest(string_to_array(elements, ',')) AS elem
from myTable

id | elem
---+-----
1  | ab
1  | cd
1  | efg
1  | hi
2  | jk
...

如何包含元素编号?IE:

id | elem | nr
---+------+---
1  | ab   | 1
1  | cd   | 2
1  | efg  | 3
1  | hi   | 4
2  | jk   | 1
...

我想要源字符串中每个元素的原始位置。我尝试过使用窗口函数(row_number()rank()),但我总是得到1. 也许是因为它们在源表的同一行?

我知道这是一个糟糕的桌子设计。这不是我的,我只是想解决它。

4

6 回答 6

217

Postgres 9.4 或更高版本

用于WITH ORDINALITY设置返回函数:

FROM子句中的函数以 为后缀时WITH ORDINALITY,会在输出中附加一 bigint列,该列从 1 开始,并为函数输出的每一行增加 1。这在集合返回函数的情况下最有用,例如unnest().

结合LATERALpg 9.3+ 中的特性,根据pgsql-hackers 上的这个线程,上面的查询现在可以写成:

SELECT t.id, a.elem, a.nr
FROM   tbl AS t
LEFT   JOIN LATERAL unnest(string_to_array(t.elements, ','))
                    WITH ORDINALITY AS a(elem, nr) ON TRUE;

LEFT JOIN ... ON TRUE保留左侧表中的所有行,即使右侧的表表达式不返回任何行。如果这无关紧要,您可以使用这种其他等效的、不那么冗长的形式和隐式CROSS JOIN LATERAL

SELECT t.id, a.elem, a.nr
FROM   tbl t, unnest(string_to_array(t.elements, ',')) WITH ORDINALITY a(elem, nr);

或者如果基于实际数组arr作为数组列)更简单:

SELECT t.id, a.elem, a.nr
FROM   tbl t, unnest(t.arr) WITH ORDINALITY a(elem, nr);

甚至,用最少的语法:

SELECT id, a, ordinality
FROM   tbl, unnest(arr) WITH ORDINALITY a;

a自动为表列别名。添加的序数列的默认名称是ordinality。但添加显式列别名和表限定列会更好(更安全、更简洁)。

Postgres 8.4 - 9.3

根据row_number() OVER (PARTITION BY id ORDER BY elem)排序顺序获得数字,而不是字符串中原始序数位置的序数。

您可以简单地省略ORDER BY

SELECT *, row_number() OVER (PARTITION by id) AS nr
FROM  (SELECT id, regexp_split_to_table(elements, ',') AS elem FROM tbl) t;

虽然这通常有效,而且我从未见过它在简单查询中失败,但 PostgreSQL 对没有ORDER BY. 由于实现细节,它恰好可以工作。

为了保证空格分隔的字符串中元素的序数

SELECT id, arr[nr] AS elem, nr
FROM  (
   SELECT *, generate_subscripts(arr, 1) AS nr
   FROM  (SELECT id, string_to_array(elements, ' ') AS arr FROM tbl) t
   ) sub;

或者如果基于实际数组则更简单:

SELECT id, arr[nr] AS elem, nr
FROM  (SELECT *, generate_subscripts(arr, 1) AS nr FROM tbl) t;

dba.SE 上的相关答案:

Postgres 8.1 - 8.4

这些功能均不可用,但:RETURNS TABLE, generate_subscripts(), unnest(), array_length(). 但这有效:

CREATE FUNCTION f_unnest_ord(anyarray, OUT val anyelement, OUT ordinality integer)
  RETURNS SETOF record
  LANGUAGE sql IMMUTABLE AS
'SELECT $1[i], i - array_lower($1,1) + 1
 FROM   generate_series(array_lower($1,1), array_upper($1,1)) i';

请特别注意,数组索引可能与元素的序数位置不同。考虑这个带有扩展功能的演示

CREATE FUNCTION f_unnest_ord_idx(anyarray, OUT val anyelement, OUT ordinality int, OUT idx int)
  RETURNS SETOF record
  LANGUAGE sql IMMUTABLE AS
'SELECT $1[i], i - array_lower($1,1) + 1, i
 FROM   generate_series(array_lower($1,1), array_upper($1,1)) i';

SELECT id, arr, (rec).*
FROM  (
   SELECT *, f_unnest_ord_idx(arr) AS rec
   FROM  (VALUES (1, '{a,b,c}'::text[])  --  short for: '[1:3]={a,b,c}'
               , (2, '[5:7]={a,b,c}')
               , (3, '[-9:-7]={a,b,c}')
      ) t(id, arr)
   ) sub;

 id |       arr       | val | ordinality | idx
----+-----------------+-----+------------+-----
  1 | {a,b,c}         | a   |          1 |   1
  1 | {a,b,c}         | b   |          2 |   2
  1 | {a,b,c}         | c   |          3 |   3
  2 | [5:7]={a,b,c}   | a   |          1 |   5
  2 | [5:7]={a,b,c}   | b   |          2 |   6
  2 | [5:7]={a,b,c}   | c   |          3 |   7
  3 | [-9:-7]={a,b,c} | a   |          1 |  -9
  3 | [-9:-7]={a,b,c} | b   |          2 |  -8
  3 | [-9:-7]={a,b,c} | c   |          3 |  -7

比较:

于 2012-01-07T04:49:48.423 回答
9

尝试:

select v.*, row_number() over (partition by id order by elem) rn from
(select
    id,
    unnest(string_to_array(elements, ',')) AS elem
 from myTable) v
于 2012-01-06T15:50:13.060 回答
6

使用下标生成函数
http://www.postgresql.org/docs/current/static/functions-srf.html#FUNCTIONS-SRF-SUBSCRIPTS

例如:

SELECT 
  id
  , elements[i] AS elem
  , i AS nr
FROM
  ( SELECT 
      id
      , elements
      , generate_subscripts(elements, 1) AS i
    FROM
      ( SELECT
          id
          , string_to_array(elements, ',') AS elements
        FROM
          myTable
      ) AS foo
  ) bar
;

更简单地说:

SELECT
  id
  , unnest(elements) AS elem
  , generate_subscripts(elements, 1) AS nr
FROM
  ( SELECT
      id
      , string_to_array(elements, ',') AS elements
    FROM
      myTable
  ) AS foo
;
于 2012-12-27T11:57:18.043 回答
3

如果元素的顺序不重要,你可以

select 
  id, elem, row_number() over (partition by id) as nr
from (
  select
      id,
      unnest(string_to_array(elements, ',')) AS elem
  from myTable
) a
于 2012-01-06T15:51:11.480 回答
1

我认为这是相关的,使用相关子查询将任意排名/序数值分配给最终集合。使用 PG 数组处理来 De-Pivot 数据集(使用 PG 9.4 工作)更像是一种实际应用用途。

WITH _students AS ( /** CTE **/
                  SELECT * FROM
                    (   SELECT 'jane'::TEXT ,'doe'::TEXT , 1::INT 
                         UNION
                        SELECT 'john'::TEXT ,'doe'::TEXT , 2::INT 
                         UNION
                        SELECT 'jerry'::TEXT ,'roe'::TEXT , 3::INT 
                         UNION
                        SELECT 'jodi'::TEXT ,'roe'::TEXT , 4::INT 
                    ) s ( fn, ln, id )
) /** end WITH **/   
SELECT s.id
 , ax.fanm
 , ax.anm
 , ax.val
 , ax.num
FROM _students s
,UNNEST /** MULTI-UNNEST() BLOCK **/
    (
        ( SELECT ARRAY[ fn, ln ]::text[] AS anm 
                  /** CORRELATED SUBQUERY **/
                 FROM _students s2 WHERE s2.id = s.id 
         )   
   
        ,( SELECT ARRAY[ 'first name', 'last name' ]::text[] AS fanm )  
     
        ,( SELECT ARRAY[ '9','8','7'] AS val) 
   
        ,( SELECT ARRAY[ 1,2,3,4,5   ] AS num) 
        
   ) ax (  anm, fanm, val, num )
;   

去中心化结果集:

+--+----------+-----+----+---+
|id|fanm      |anm  |val |num|
+--+----------+-----+----+---+
|2 |first name|john |9   |1  |
|2 |last name |doe  |8   |2  |
|2 |NULL      |NULL |7   |3  |
|2 |NULL      |NULL |NULL|4  |
|2 |NULL      |NULL |NULL|5  |
|1 |first name|jane |9   |1  |
|1 |last name |doe  |8   |2  |
|1 |NULL      |NULL |7   |3  |
|1 |NULL      |NULL |NULL|4  |
|1 |NULL      |NULL |NULL|5  |
|4 |first name|jodi |9   |1  |
|4 |last name |roe  |8   |2  |
|4 |NULL      |NULL |7   |3  |
|4 |NULL      |NULL |NULL|4  |
|4 |NULL      |NULL |NULL|5  |
|3 |first name|jerry|9   |1  |
|3 |last name |roe  |8   |2  |
|3 |NULL      |NULL |7   |3  |
|3 |NULL      |NULL |NULL|4  |
|3 |NULL      |NULL |NULL|5  |
+--+----------+-----+----+---+
于 2021-05-13T16:39:59.287 回答
0

unnest2()作为运动

pg v8.4 之前的旧版本需要用户定义的unnest(). 我们可以调整这个旧函数以返回具有索引的元素:

CREATE FUNCTION unnest2(anyarray)
  RETURNS setof record  AS
$BODY$
  SELECT $1[i], i
  FROM   generate_series(array_lower($1,1),
                         array_upper($1,1)) i;
$BODY$ LANGUAGE sql IMMUTABLE;
于 2015-07-05T11:13:43.280 回答