multiple select query with same where clause - oracle

Question

I have two type of select statement with the same complicated where clause.
One - Returns transaction detailed data
select field_1, field_2, field_3, ... , field_30 from my_table where my_where_clause
Second - Returns transaction data grouped by(distinct) merchants
select distinct field_1, field_2, field_8 from my_table where my_where_clause
Statements are called separately.
I want to simplify my code and not to repeat this complicated where clause in both statements without loosing performance
In dynamic SQL it's possible but I don't want to use dynamic SQL.
Any suggestions?

Answer 1

Suggestion: you can try GROUPING SETS expression.
It allows you to selectively specify the set of groups that you want to create within a GROUP BY clause. In
In your case, you can specify 2 sets, one group by set for all fields from 1 to 30 and another set for fields 1,2&8.
Link- https://docs.oracle.com/cd/E40518_01/server.761/es_eql/src/reql_aggregation_grouping_sets.html
However, it will return the output of both the groups in a single resultset, not sure if this fits in your design.

Answer 2

So you could encapsulate this statement, in a view or function, e,g,:
create or replace view view_1 as
select field_1, field_2, field_3, ... , field_30
from my_table
where my_where_clause
Then your second query could be
select distinct * from view_1;

Answer 3

You said that you are using this query from java. Try this.
create or replace function get_cursor(p_type varchar2 default null/* other paramethers*/ ) return sys_refcursor
is
result_curosr sys_refcursor;
begin
open result_curosr for 'select '||p_type||' object_type,status from user_objects' /* where clausele */ ;
return result_curosr;
end;
And usage of this from java.
Connection con = ...
CallableStatement callableStatement = con.prepareCall("declare c sys_refcursor; begin ? := get_cursor(?); end ; ");
callableStatement.registerOutParameter(1, OracleTypes.CURSOR);
callableStatement.setString(2, "Distinct"); // for distinct
or
callableStatement.setNull(2, OracleTypes.VARCHAR); // for full results
callableStatement.executeUpdate();
ResultSet rs = (ResultSet) callableStatement.getObject(1);
while(rs.next()) {
System.err.println(rs.getString(1));
}
rs.close();
con.close();
Other solution.
Add one more parameter and do simple deduplication using all columns from query. But i don't see any advantages.
select object_type,status from
(select object_type,status, row_number() over( partition by object_type,status order by 1) rn from user_objects /* your_where_clusue */
) where rn = case when 'DISTIINCT'/* <- paramete here :isDistinct */ = 'DISTIINCT' then 1 else rn end;

Answer 4

You can make dynamic SQL more readable by using multi-line strings, alternative quotes, and templates.
declare
v_select varchar2(32767);
v_where varchar2(32767);
v_code varchar2(32767) := '
##SELECT##
##WHERE##
';
begin
--Populate the clauses.
if ... then
v_select := 'select field_1, field_2, field_3, ... , field_30 from my_table';
else
v_select := 'select distinct field_1, field_2, field_8 from my_table';
end if;
if ... then
v_where :=
q'[
where field_1 = 'foo'
and field_2 = :bind1
...
]';
else
v_where :=
q'[
where field_2 = 'bar'
and field_2 = :bind2
...
]';
end if;
--Fill in the code.
v_code := replace(v_code, '##SELECT##', v_select);
v_code := replace(v_code, '##WHERE##', v_where);
--Print the code to check the formatting. Remove after testing.
dbms_output.put_line(v_code);
--Run it.
execute immediate v_code using ...;
end;
/
It's not perfect but it prevents ugly concatenation. And it's much better than the anti-patterns needed to avoid dynamic SQL at all costs. In most languages features like polymorphism and reflection are better than dynamic code. PL/SQL does not have good support for those advanced features so it's usually better to build the code as a string.