Oracle Lag function with dynamic parameter

Question

I have a specific problem. I have a table which contains invalid values. I need to replace the invalid values (here 0) with the previous value which is bigger than 0.

The difficulty is, it is not appropiate for me to use an Update or an insert(Cursor and update would do it).Well my only way is to use a Select statement.

When I use the lag(col1, 1) - function with when case, I get only one column with the correct value.

select col1, col2 realcol2,  
(case 
  when col2 = 0 then 
    lag(col2,1,1) over (partition by col1 order by col1 )
  else
   col2
  end ) col2,     
col3 realcol3,
(case 
  when col3 = 0 then 
    lag(col3,1,1) over (partition by col1 order by col1 )
  else
   col3
  end ) col3
from test_table 

Contents of TEST_TABLE:

---------------------------
 Col1 | Col2 | Col3 | Col4
---------------------------
  A   |  0   |  1   |  5
  B   |  0   |  4   |  0
  C   |  2   |  0   |  0
  D   |  0   |  0   |  0
  E   |  3   |  5   |  0
  F   |  0   |  3   |  0
  G   |  0   |  3   |  1
  A   |  0   |  1   |  5
  E   |  3   |  5   |  0

Expected query result:

---------------------------
 Col1 | Col2 | Col3 | Col4
---------------------------
  A   |  0   |  1   |  5
  B   |  0   |  4   |  5
  C   |  2   |  4   |  5
  D   |  2   |  4   |  5
  E   |  3   |  5   |  5
  F   |  3   |  3   |  5
  G   |  3   |  3   |  1
  A   |  3   |  1   |  5
  E   |  3   |  5   |  5

Answer 1

SELECT col1,
       CASE col2 WHEN 0 THEN NVL( LAG( CASE col2 WHEN 0 THEN NULL ELSE col2 END ) IGNORE NULLS OVER ( ORDER BY NULL ), 0 ) ELSE col2 END AS col2,
       CASE col3 WHEN 0 THEN NVL( LAG( CASE col3 WHEN 0 THEN NULL ELSE col3 END ) IGNORE NULLS OVER ( ORDER BY NULL ), 0 ) ELSE col3 END AS col3,
       CASE col4 WHEN 0 THEN NVL( LAG( CASE col4 WHEN 0 THEN NULL ELSE col4 END ) IGNORE NULLS OVER ( ORDER BY NULL ), 0 ) ELSE col4 END AS col4
FROM   table_name;

Result:

COL1       COL2       COL3       COL4
---- ---------- ---------- ----------
A             0          1          5 
B             0          4          5 
C             2          4          5 
D             2          4          5 
E             3          5          5 
F             3          3          5 
G             3          3          1 
A             3          1          5 
E             3          5          5

Answer 2

I'm assuming an additional column col0 that contains an obvious ordering criteria for your data, as your col1 example data isn't really ordered correctly (repeated, trailing values of A and E).

I love the MODEL clause for these kinds of purposes. The following query yields the expected result:

WITH t(col0, col1, col2, col3, col4) AS (
  SELECT 1, 'A', 0, 1, 5 FROM DUAL UNION ALL
  SELECT 2, 'B', 0, 4, 0 FROM DUAL UNION ALL
  SELECT 3, 'C', 2, 0, 0 FROM DUAL UNION ALL
  SELECT 4, 'D', 0, 0, 0 FROM DUAL UNION ALL
  SELECT 5, 'E', 3, 5, 0 FROM DUAL UNION ALL
  SELECT 6, 'F', 0, 3, 0 FROM DUAL UNION ALL
  SELECT 7, 'G', 0, 3, 1 FROM DUAL UNION ALL
  SELECT 8, 'A', 0, 1, 5 FROM DUAL UNION ALL
  SELECT 9, 'E', 3, 5, 0 FROM DUAL
)
SELECT * FROM t
MODEL
  DIMENSION BY (row_number() OVER (ORDER BY col0) rn)
  MEASURES (col1, col2, col3, col4)
  RULES (
    col2[any] = DECODE(col2[cv(rn)], 0, NVL(col2[cv(rn) - 1], 0), col2[cv(rn)]),
    col3[any] = DECODE(col3[cv(rn)], 0, NVL(col3[cv(rn) - 1], 0), col3[cv(rn)]),
    col4[any] = DECODE(col4[cv(rn)], 0, NVL(col4[cv(rn) - 1], 0), col4[cv(rn)])
  )

Result:

RN   COL1  COL2  COL3  COL4
1    A     0     1     5
2    B     0     4     5
3    C     2     4     5
4    D     2     4     5
5    E     3     5     5
6    F     3     3     5
7    G     3     3     1
8    A     3     1     5
9    E     3     5     5

SQLFiddle

A note on the MODEL clause vs. window function-based approaches

While the above looks cool (or scary, depending on your point of view), you should certainly prefer using a window function based appraoch as exposed by the other elegant answers by nop77svk (using LAST_VALUE() IGNORE NULLS) or MT0 (using LAG() IGNORE NULLS). I've explained these answers more in detail in this blog post.

Answer 3

Assuming you want the previous values as per your original data order (whatever that might be), then your query might look like:

with preserve_the_order$ as (
    select X.*,
        rownum as original_order$
    from test_table X
)
select X.col1,
    nvl(last_value(case when col2 > 0 then col2 end) ignore nulls over (order by original_order$ rows between unbounded preceding and current row), col2) as col2,
    nvl(last_value(case when col3 > 0 then col3 end) ignore nulls over (order by original_order$ rows between unbounded preceding and current row), col3) as col3,
    nvl(last_value(case when col4 > 0 then col4 end) ignore nulls over (order by original_order$ rows between unbounded preceding and current row), col4) as col4
from preserve_the_order$ X
order by original_order$
;

Result:

COL1       COL2       COL3       COL4
---- ---------- ---------- ----------
A             0          1          5
B             0          4          5
C             2          4          5
D             2          4          5
E             3          5          5
F             3          3          5
G             3          3          1
A             0          1          5
E             3          5          5