如何在PostgreSQL中創建一個WINDOWS直到再次出現相同的值？

Question

我想在PostgreSQL中創建一個WINDOW，並從數字中獲取row_number()，直到它再次出現。作爲例子，假設我要創建79個窗口，直到79再次出現，並重置計數，它必須是這樣的：

number  must be  row_number number 
    50        ?  50 
    79        1  79 
    85        2  85 
    74        3  74 
    14        4  14 
    79        1  79 
    46        2  46 
    85        3  85 
    79        1  79 
    45        2  45 

我怎樣才能做到這一點？

Answer 1

考慮一下：

-- temporary test table 
CREATE TEMP TABLE tbl (id serial, nr int); 
INSERT INTO tbl(nr) VALUES 
(50),(79),(85),(74),(14) 
,(79),(46),(85),(79),(45); 

SELECT id, nr 
     ,CASE WHEN grp > 0 THEN 
      row_number() OVER (PARTITION BY grp ORDER BY id)::text 
     ELSE '?' END AS rn  
FROM (
    SELECT id, nr 
      ,sum(CASE WHEN nr = 79 THEN 1 ELSE 0 END) OVER (ORDER BY id) AS grp 
    FROM tbl) x 
-- WHERE grp > 0 -- to exclude numbers before the first 79 

正好產生你的結果。

Answer 2

總有一個CTE潛伏的地方......

-- temporary test table 
-- (thanks for that) 
CREATE TEMP TABLE tbl (id serial, nr int); 
INSERT INTO tbl(nr) VALUES 
(50),(79),(85),(74),(14) 
,(79),(46),(85),(79),(45); 

-- EXPLAIN ANALYZE 
WITH next AS (
    SELECT t1.id AS id 
     , t2.id AS next 
    FROM tbl t1 
    JOIN tbl t2 ON (t2.nr = t1.nr AND t2.id > t1.id) 
     WHERE NOT EXISTS (SELECT * 
      FROM tbl nx 
      WHERE nx.nr = t1.nr 
      AND nx.id > t1.id 
      AND nx.id < t2.id 
      ) 
    ) 
SELECT t0.id 
     , t0.nr 
     , next.next AS next 
FROM tbl t0 
LEFT JOIN next ON (next.id=t0.id) 
ORDER BY id 
    ;