過濾順序數據

Question

我有以下查詢（例如發現這里產生的序列號來標記位置的每個變化對這個論壇）。

WITH t(ID, col1  ,Location) AS (
select 1, 1 , 1 union all  
select 1, 2 , 1 union all  
select 1, 3 , 2 union all  
select 1, 4 , 2 union all  
select 1, 5 , 1 union all  
select 1, 6 , 2 union all  
select 1, 7 , 2 union all  
select 1, 8 , 3 union all 
select 2, 1 , 1 union all  
select 2, 2 , 2 union all  
select 2, 3 , 2 union all  
select 2, 4 , 2 union all  
select 2, 5 , 1 union all  
select 2, 6 , 1 union all  
select 2, 7 , 2 union all  
select 2, 8 , 3
)
SELECT t.ID, t.col1, t.Location,
    sum(x) OVER (partition by ID order by col1) sequence
FROM (
    SELECT t.*,
        CASE WHEN Location = lag(Location) OVER (order by ID, col1) THEN 0
            ELSE 1
        END x
    FROM t
    ) t
ORDER BY ID, col1
;

現在，我只想保留那些表示每個ID通過不同位置的順序路徑的行。 如何相應地過濾數據，以便產生以下結果：

ID  Location
1   1
1   2
1   1
1   2
1   3
2   1
2   2
2   1
2   2
2   3

有沒有辦法實現他的目標？

Answer 1

您似乎想刪除相鄰的重復項：

SELECT t.ID, t.col1, t.Location
FROM (SELECT t.*,
             (CASE WHEN Location = lag(Location) OVER (order by ID, col1) THEN 0
                   ELSE 1
              END) x
      FROM t
     ) t
WHERE x = 1
ORDER BY ID, col1;

我使用了查詢的結構。 我實際上會這樣寫：

SELECT t.ID, t.col1, t.Location
FROM (SELECT t.*,
            lag(Location) OVER (order by ID, col1) as prev_location
      FROM t
     ) t
WHERE prev_location is NULL or prev_location <> location
ORDER BY ID, col1;