Need help with writing a query with dynamic FROM clause

Question

Hi Folks,
I need help with an query that should generate the "FROM" clause dynamically.
My main query is as follows
select DT_SKEY, count(*)
from *???*
where DT_SKEY between 20110601 and 20110719
group by DT_SKEY
having count(*) = 0
order by 1; The "from" clause of the above query should be generated as below
select 'Schema_Name'||'.'||TABLE_NAME
from dba_tables
where OWNER = 'Schema_Name'Simply sticking the later query in the first query does not work.
Any pointers will be appreciated.
Thanks
rogers42

Answer 1

Hi,
rogers42 wrote:
Hi Folks,
I need help with an query that should generate the "FROM" clause dynamically.
My main query is as follows
select DT_SKEY, count(*)
from *???*
where DT_SKEY between 20110601 and 20110719
group by DT_SKEY
having count(*) = 0
order by 1; The "from" clause of the above query should be generated as below
select 'Schema_Name'||'.'||TABLE_NAME
from dba_tables
where OWNER = 'Schema_Name'
Remember that anything inside quotes is case-sensitive. Is the owner really "Schema_Name" with a capital S and a capital N, and 8 lower-case letters?
Simply sticking the later query in the first query does not work.Right; the table name must be given when you compile the query. It's not an expression that you can generate in the query itself.
Any pointers will be appreciated.In SQL*Plus, you can do something like the query bleow.
Say you want to count the rows in scott.emp, but you're not certain that the name is emp; it could be emp_2011 or emp_august, or anything else that starts with e. (And the name could change every day, so you can't just look it up now and hard-code it in a query that you want to run in the future.)
Typically, how dynamic SQL works is that some code (such as a preliminary query) gets some of the information you need to write the query first, and you use that information in a SQL statement that is compiled and run after that. For example:
-- Preliminary Query:
COLUMN     my_table_name_col     NEW_VALUE my_table_name
SELECT     table_name     AS my_table_name_col
FROM     all_tables
WHERE     owner          = 'SCOTT'
AND     table_name     LIKE 'E%';
-- Main Query:
SELECT     COUNT (*)     AS cnt
FROM     scott.&my_table_name
;This assumes that the preliminary query will find exactly one row; that is, it assumes that SCOTT has exactly one table whose name starts with E. Could you have 0 tables in the schema, or more than 1? If so, what results would you want? Give a concrete example, preferably suing commonly available tables (like those in the SCOTT schema) so that the poepl who want to help you can re-create the problem and test their ideas.
Edited by: Frank Kulash on Aug 11, 2011 2:30 PM