How to sort by dynamic column in oracle? - sql

Question

I have some complex oracle query, but I will try to make it simple. I have something like this:
SELECT TBL1.*, TBL2.*
FROM TABLE_1 TBL1
LEFT JOIN (
SELECT *
FROM
(
SELECT TBL2.VERSION_ID, TBL2.CONFIG_ID, TBL2.VALUE
FROM TABLE_2 TBL2
)
PIVOT
(
MAX(VALUE) FOR CONFIG_ID IN (:metadataClassConfigs)
)
) TBL2 ON TBL1.VERSION_ID = TBL2.VERSION_ID
ORDER BY
CASE
WHEN :orderByCustomClass IS NOT NULL THEN
CASE
WHEN :orderByCustomClass = 1 THEN TBL2."1"
WHEN :orderByCustomClass = 21 THEN TBL2."21"
WHEN :orderByCustomClass = 22 THEN TBL2."22"
WHEN :orderByCustomClass = 23 THEN TBL2."23"
WHEN :orderByCustomClass = 24 THEN TBL2."24"
WHEN :orderByCustomClass = 25 THEN TBL2."25"
WHEN :orderByCustomClass = 26 THEN TBL2."26"
WHEN :orderByCustomClass = 27 THEN TBL2."27"
WHEN :orderByCustomClass = 28 THEN TBL2."28"
WHEN :orderByCustomClass = 29 THEN TBL2."29"
WHEN :orderByCustomClass = 30 THEN TBL2."30"
WHEN :orderByCustomClass = 31 THEN TBL2."31"
WHEN :orderByCustomClass = 32 THEN TBL2."32"
WHEN :orderByCustomClass = 34 THEN TBL2."34"
WHEN :orderByCustomClass = 35 THEN TBL2."35"
WHEN :orderByCustomClass = 36 THEN TBL2."36"
WHEN :orderByCustomClass = 41 THEN TBL2."41"
WHEN :orderByCustomClass = 52 THEN TBL2."42"
END
END;
and this is working fine. This input parameters are: :metadataClassConfigs is the list of numbers (1,21,22,23,24,25,26,27,28,29,30,31,32,34,35,36,41,42) and :orderByCustomClass can be any of this number.
I have much more numbers then this list, more than 1000, so I am wondering how can I order by dynamic column something like:
WHEN :orderByCustomClass IS NOT NULL THEN TBL2."{:orderByCustomClass}"
?

Answer 1

There is a multiple way for dynamic SQL in Oracle PL/SQL. I'm assuming that you are talking about PL/SQL, because in other kind of clients (like python-oracle, jdbc) the only way to send a "query" is to create cursor from string. So you've always forced to build query kind of dynamically...
Native Dynamic SQL - execute immediate
Good for simple cases (look how to get the result - works best for one row - its more complicated for arrays).
The query is a string - so you can "build" it. If you need - you can use parameters with USING clause (each parameter in query must have colon as a prefix). Be aware that they are mapped by position in query - not by name.
declare
type t_rec is record (
<describe returned columns>
);
type t_result_array is table of t_rec index by pls_integer;
v_result_array t_result_array;
v_sort_column varchar2(4000);
begin
-- do some logic to determine name of column for order by:
v_sort_column := <some_logic determining column name for sorting>;
-- if logic is based on raw user input, then you should sanitize it:
v_sort_column := DBMS_ASSERT.QUALIFIED_SQL_NAME(v_sort_column);
-- build query based on v_sort_column value
execute immediate 'select ... from ...
order by '||v_sort_column
bulk collect into v_result_array;
<do something with result stored in v_result_array>
end;
/
Native Dynamic SQL - OPEN FOR
Very similar to execute immediate but based on cursor variable and OPEN FOR statement. To accomplish it you have to do 3 steps: open cursor, fetch rows and close cursor.
declare
type t_rec is record (
<describe returned columns>
);
type t_result_array is table of t_rec index by pls_integer;
v_result_array t_result_array;
v_sort_column varchar2(4000);
type t_ret_cursor is ref cursor return t_rec;
v_cursor t_ret_cursor;
begin
-- do some logic to determine name of column for order by:
v_sort_column := <some_logic determining column name for sorting>;
-- if logic is based on raw user input, then you should sanitize it:
v_sort_column := DBMS_ASSERT.QUALIFIED_SQL_NAME(v_sort_column);
open v_cursor for 'select ... from ...
order by '||v_sort_column;
fetch v_cursor bulk collect into v_cursor;
close v_cursor;
<do something with result stored in v_result_array>
end;
/
Dynamic SQL - DBMS_SQL package
This is the most flexible way of doing it - you can even conditionally change selected columns or dynamically check what kind of row is in result (number of columns, data types etc.). Furthermore, it is also one of the best in terms of performance.
I'm just putting information about this option here so you can see for yourself if you need these features and capabilities.
There are many more steps here and they are more complex: open cursor, parse, bind every parameter (optional), define columns, execute, fetch, access data, so I will not post any example. Probably it's an overkill for your purposes.