I'm using pivot in Oracle PL SQL Developer as follows:
SELECT *
FROM population
PIVOT (AVG(Total) for Data_Type IN ('Group1','Group2','Group3'))
This works fine, but I don't want to have to edit every time a new column is added or one is changed (i.e. Group4, 5, 6 etc), so I tried a sub-query as follows:
SELECT *
FROM population
PIVOT (AVG(Total) for Data_Type IN (SELECT Data_Type FROM population))
This results in the following error: ORA-00936: missing expression.
After some research, it appears that I can generate the results with XML, so I tried the following:
SELECT *
FROM population
PIVOT XML(AVG(Total) for Data_Type IN (ANY))
This actually generates the desired data, but in XML format. So my question is, how can I convert the XML results into standard table format within PL SQL Developer? Or, if I want to bring the generated XML file into a tool like Crystal Reports, I need to have a schema file for these results. Is that something that can easily be auto generated within the SQL?
Would you consider using PIPELINED function to achieve your goal?
I have written a an example of such a function. The example is based on the table, sample data and PIVOT
query from Tom Kyte's articles which you can find on his site:
Tom Kyte's article about PIVOT/UNPIVOT
Tom Kyte's article about PIPELINED functions
The example works as follows.
We create two types:
Then we create a PIPELINED function which contains the query with PIVOT
, which generates XML (so you do not have to hard-code the values you want to pivot over). This function extracts data from generated XML and passes (PIPEs) rows to the calling query as they are generated (on the fly - they are not generated all at once which is important for performance).
Finally, you write a query which selects records from that function (at the end is an example of such a query).
CREATE TABLE pivot_test (
id NUMBER,
customer_id NUMBER,
product_code VARCHAR2(5),
quantity NUMBER
);
INSERT INTO pivot_test VALUES (1, 1, 'A', 10);
INSERT INTO pivot_test VALUES (2, 1, 'B', 20);
INSERT INTO pivot_test VALUES (3, 1, 'C', 30);
INSERT INTO pivot_test VALUES (4, 2, 'A', 40);
INSERT INTO pivot_test VALUES (5, 2, 'C', 50);
INSERT INTO pivot_test VALUES (6, 3, 'A', 60);
INSERT INTO pivot_test VALUES (7, 3, 'B', 70);
INSERT INTO pivot_test VALUES (8, 3, 'C', 80);
INSERT INTO pivot_test VALUES (9, 3, 'D', 90);
INSERT INTO pivot_test VALUES (10, 4, 'A', 100);
COMMIT;
CREATE TYPE t_pivot_test_obj AS OBJECT (
customer_id NUMBER,
product_code VARCHAR2(5),
sum_quantity NUMBER
);
/
CREATE TYPE t_pivot_test_obj_tab IS TABLE OF t_pivot_test_obj;
/
CREATE OR REPLACE FUNCTION extract_from_xml RETURN t_pivot_test_obj_tab PIPELINED
AS
v_xml XMLTYPE;
v_item_xml XMLTYPE;
v_index NUMBER;
v_sum_quantity NUMBER;
CURSOR c_customer_items IS
SELECT customer_id, product_code_xml
FROM (SELECT customer_id, product_code, quantity
FROM pivot_test)
PIVOT XML (SUM(quantity) AS sum_quantity FOR (product_code) IN (SELECT DISTINCT product_code
FROM pivot_test));
BEGIN
-- loop through all records returned by query with PIVOT
FOR v_rec IN c_customer_items
LOOP
v_xml := v_rec.product_code_xml;
v_index := 1;
-- loop through all ITEM elements for each customer
LOOP
v_item_xml := v_xml.EXTRACT('/PivotSet/item[' || v_index || ']');
EXIT WHEN v_item_xml IS NULL;
v_index := v_index + 1;
IF v_item_xml.EXTRACT('/item/column[@name="SUM_QUANTITY"]/text()') IS NOT NULL THEN
v_sum_quantity := v_item_xml.EXTRACT('/item/column[@name="SUM_QUANTITY"]/text()').getNumberVal();
ELSE
v_sum_quantity := 0;
END IF;
-- finally, for each customer and item - PIPE the row to the calling query
PIPE ROW(t_pivot_test_obj(v_rec.customer_id,
v_item_xml.EXTRACT('/item/column[@name="PRODUCT_CODE"]/text()').getStringVal(),
v_sum_quantity));
END LOOP;
END LOOP;
END;
/
SELECT customer_id, product_code, sum_quantity
FROM TABLE(extract_from_xml())
;
Output:
CUSTOMER_ID PRODUCT_CODE SUM_QUANTITY
---------------------- ------------ ----------------------
1 A 10
1 B 20
1 C 30
1 D 0
2 A 40
2 B 0
2 C 50
2 D 0
3 A 60
3 B 70
3 C 80
3 D 90
4 A 100
4 B 0
4 C 0
4 D 0
16 rows selected
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