XMLTABLE / XQUERY performance

Question

Hi all,
Below is a sample XML representing a spreadsheet :
<Table>
<Row>
  <Cell><Data>1</Data></Cell>
  <Cell><Data>A</Data></Cell>
  <Cell><Data>B</Data></Cell>
  <Cell Index="5"><Data>D</Data></Cell>
</Row>
<Row>
  <Cell><Data>2</Data></Cell>
  <Cell Index="3"><Data>B</Data></Cell>
  <Cell><Data>C</Data></Cell>
</Row>
<Row>
  <Cell><Data>3</Data></Cell>
  <Cell Index="3"><Data>B</Data></Cell>
  <Cell Index="5"><Data>D</Data></Cell>
</Row>
<Row>
  <Cell><Data>4</Data></Cell>
  <Cell><Data>A</Data></Cell>
  <Cell><Data>B</Data></Cell>
  <Cell><Data>C</Data></Cell>
  <Cell><Data>D</Data></Cell>
</Row>
<Row>
  <Cell><Data>5</Data></Cell>
  <Cell><Data>A</Data></Cell>
  <Cell Index="4"><Data>C</Data></Cell>
  <Cell><Data>D</Data></Cell>
</Row>
</Table>which should be interpreted as :
cols --> 1 2 3 4 5
         1 A B   D
         2   B C
         3   B   D
         4 A B C D
         5 A   C DAs you can see, for each row, empty cells are simply omitted in the document.
The next non-empty cell is then marked with an Index attribute representing its true position on the row.
My requirement is to query the document and access the values based on cells positions on the row.
Because of empty cells, Data values cannot be accessed by a simple xpath like "/Cell[n]/Data".
So I came up with the following :
WITH t AS (
select xmltype(
'<Table>
<Row>
  <Cell><Data>1</Data></Cell>
  <Cell><Data>A</Data></Cell>
  <Cell><Data>B</Data></Cell>
  <Cell Index="5"><Data>D</Data></Cell>
</Row>
<Row>
  <Cell><Data>2</Data></Cell>
  <Cell Index="3"><Data>B</Data></Cell>
  <Cell><Data>C</Data></Cell>
</Row>
<Row>
  <Cell><Data>3</Data></Cell>
  <Cell Index="3"><Data>B</Data></Cell>
  <Cell Index="5"><Data>D</Data></Cell>
</Row>
<Row>
  <Cell><Data>4</Data></Cell>
  <Cell><Data>A</Data></Cell>
  <Cell><Data>B</Data></Cell>
  <Cell><Data>C</Data></Cell>
  <Cell><Data>D</Data></Cell>
</Row>
<Row>
  <Cell><Data>5</Data></Cell>
  <Cell><Data>A</Data></Cell>
  <Cell Index="4"><Data>C</Data></Cell>
  <Cell><Data>D</Data></Cell>
</Row>
</Table>') doc from dual
SELECT x.*
FROM t, xmltable(
'for $j in /Table/Row
return <ROW> {
   for $i at $pos in $j/Cell
   let $x := $j/Cell[position()<=$pos and @Index][last()]/@Index
   let $x2 := if($x) then $x else 1
   let $p := count($j/Cell[@Index=$x]/preceding-sibling::*)+1
   return <DATA pos="{$pos - $p + $x2}">{$i/Data/text()}</DATA>
} </ROW>'
PASSING t.doc
COLUMNS cell1 number      PATH '/ROW/DATA[@pos="1"]',
         cell2 varchar2(1) PATH '/ROW/DATA[@pos="2"]',
         cell3 varchar2(1) PATH '/ROW/DATA[@pos="3"]',
         cell4 varchar2(1) PATH '/ROW/DATA[@pos="4"]',
         cell5 varchar2(1) PATH '/ROW/DATA[@pos="5"]'
) x;Basically, the XQUERY reconstructs each row and gives each cell its true position. We can then access the data with a simple position predicate.
It works well for small documents, but rapidly shows awful performance as the size increases (which is understandable).
So my question : is there a better way to achieve the requirement (or to improve performance)?
Thanks a lot.
(DB version is 10.2.0.4)
Edited by: odie_63 on 28 déc. 2009 19:21

Answer 1

what if you do the logic outside of the xquery?
like this:
SQL> set timi on;
SQL> WITH t AS (
  2   select xmltype(
  3  '<Table>
  4   <Row>
  5    <Cell><Data>1</Data></Cell>
  6    <Cell><Data>A</Data></Cell>
  7    <Cell><Data>B</Data></Cell>
  8    <Cell Index="5"><Data>D</Data></Cell>
  9   </Row>
10   <Row>
11    <Cell><Data>2</Data></Cell>
12    <Cell Index="3"><Data>B</Data></Cell>
13    <Cell><Data>C</Data></Cell>
14   </Row>
15   <Row>
16    <Cell><Data>3</Data></Cell>
17    <Cell Index="3"><Data>B</Data></Cell>
18    <Cell Index="5"><Data>D</Data></Cell>
19   </Row>
20   <Row>
21    <Cell><Data>4</Data></Cell>
22    <Cell><Data>A</Data></Cell>
23    <Cell><Data>B</Data></Cell>
24    <Cell><Data>C</Data></Cell>
25    <Cell><Data>D</Data></Cell>
26   </Row>
27   <Row>
28    <Cell><Data>5</Data></Cell>
29    <Cell><Data>A</Data></Cell>
30    <Cell Index="4"><Data>C</Data></Cell>
31    <Cell><Data>D</Data></Cell>
32   </Row>
33  </Table>') doc from dual
34  )
35  SELECT x.*
36  FROM t, xmltable(
37  'for $j in /Table/Row
38   return <ROW> {
39     for $i at $pos in $j/Cell
40     let $x := $j/Cell[position()<=$pos and @Index][last()]/@Index
41     let $x2 := if($x) then $x else 1
42     let $p := count($j/Cell[@Index=$x]/preceding-sibling::*)+1
43     return <DATA pos="{$pos - $p + $x2}">{$i/Data/text()}</DATA>
44   } </ROW>'
45   PASSING t.doc
46   COLUMNS cell1 number      PATH '/ROW/DATA[@pos="1"]',
47           cell2 varchar2(1) PATH '/ROW/DATA[@pos="2"]',
48           cell3 varchar2(1) PATH '/ROW/DATA[@pos="3"]',
49           cell4 varchar2(1) PATH '/ROW/DATA[@pos="4"]',
50           cell5 varchar2(1) PATH '/ROW/DATA[@pos="5"]'
51  ) x;
     CELL1 C C C C                                                             
         1 A B   D                                                             
         2   B C                                                               
         3   B   D                                                             
         4 A B C D                                                             
         5 A   C D                                                             
Elapsed: 00:00:00.64
SQL>
SQL> WITH t AS (
  2   select xmltype('<Table>
  3   <Row>
  4    <Cell><Data>1</Data></Cell>
  5    <Cell><Data>A</Data></Cell>
  6    <Cell><Data>B</Data></Cell>
  7    <Cell Index="5"><Data>D</Data></Cell>
  8   </Row>
  9   <Row>
10    <Cell><Data>2</Data></Cell>
11    <Cell Index="3"><Data>B</Data></Cell>
12    <Cell><Data>C</Data></Cell>
13   </Row>
14   <Row>
15    <Cell><Data>3</Data></Cell>
16    <Cell Index="3"><Data>B</Data></Cell>
17    <Cell Index="5"><Data>D</Data></Cell>
18   </Row>
19   <Row>
20    <Cell><Data>4</Data></Cell>
21    <Cell><Data>A</Data></Cell>
22    <Cell><Data>B</Data></Cell>
23    <Cell><Data>C</Data></Cell>
24    <Cell><Data>D</Data></Cell>
25   </Row>
26   <Row>
27    <Cell><Data>5</Data></Cell>
28    <Cell><Data>A</Data></Cell>
29    <Cell Index="4"><Data>C</Data></Cell>
30    <Cell><Data>D</Data></Cell>
31   </Row>
32  </Table>') doc from dual)
33  select
34    case when v.cell_1_index is null then v.cell_1 end cell_one
35  , case when nvl(v.cell_1_index,-1)=2 then v.cell_1
36         when v.cell_2_index is null and v.cell_1_index is null then v.cell_2
37    end cell_two
38  , case when nvl(v.cell_1_index,-1)=3 then v.cell_1
39         when nvl(v.cell_2_index,-1)=3 then v.cell_2
40         when v.cell_1_index=2 and v.cell_2_index is null then v.cell_2
41         when coalesce(v.cell_1_index,v.cell_2_index,v.cell_3_index) is null then v.cell_3
42    end cell_three
43  , case when nvl(v.cell_1_index,-1)=4 then v.cell_1
44         when nvl(v.cell_2_index,-1)=4 then v.cell_2
45         when nvl(v.cell_3_index,-1)=4 then v.cell_3
46         when v.cell_1_index=2 and v.cell_2 is not null and v.cell_3_index is null then v.cell_3
47         when v.cell_1_index=3 and v.cell_2 is not null and v.cell_4_index is null then v.cell_2
48         when v.cell_2_index=3 and v.cell_3_index is null then v.cell_3
49         when coalesce(v.cell_1_index,v.cell_2_index,v.cell_3_index,v.cell_4_index) is null then v.cell_4
50    end cell_four
51  , case when nvl(v.cell_1_index,-1)=5 then v.cell_1
52         when nvl(v.cell_2_index,-1)=5 then v.cell_2
53         when nvl(v.cell_3_index,-1)=5 then v.cell_3
54         when nvl(v.cell_4_index,-1)=5 then v.cell_4
55         when v.cell_1_index=3 and v.cell_2_index is null then v.cell_3
56         when v.cell_1_index=4 then v.cell_2
57         when v.cell_3_index=4 then v.cell_4
58         when v.cell_2_index=3 and v.cell_3_index is null and v.cell_4_index is null then v.cell_4
59         when coalesce(v.cell_1_index,v.cell_2_index,v.cell_3_index,v.cell_4_index) is null then v.cell_5
60    end cell_five
61  from
62  t,xmltable('/Table/Row'
63  passing t.doc
64  columns
65   cell_1 varchar2(10) path 'Cell[1]/Data'
66  ,cell_1_index number path 'Cell[1]/@Index'
67  ,cell_2 varchar2(10) path 'Cell[2]/Data'
68  ,cell_2_index number path 'Cell[2]/@Index'
69  ,cell_3 varchar2(10) path 'Cell[3]/Data'
70  ,cell_3_index number path 'Cell[3]/@Index'
71  ,cell_4 varchar2(10) path 'Cell[4]/Data'
72  ,cell_4_index number path 'Cell[4]/@Index'
73  ,cell_5 varchar2(10) path 'Cell[5]/Data'
74  ) v;
CELL_ONE   CELL_TWO   CELL_THREE CELL_FOUR  CELL_FIVE                          
1          A          B                     D                                  
2                     B          C                                             
3                     B                     D                                  
4          A          B          C          D                                  
5          A                     C          D                                  
Elapsed: 00:00:00.04
SQL> spool off;Edited by: Ants Hindpere on Mar 10, 2010 1:03 AM