postgres sql / dbweaver - Using a variable for tablename? - sql

Question

One of the SQL Queries use the same table name again and again -
Example -
select
rr.jdoc as child_node, json_agg(parent_rr.jdoc)::jsonb as parent_node , array_length(array_agg(parent_rr.jdoc)::jsonb[], 1) as count
from MYTABLE rr, MYTABLE parent_rr
where
parent_rr.jdoc #> (rr.jdoc->'somefield')::jsonb
group by rr.jdoc
UNION
select rr.jdoc, NULL as parent_id, null as pcount
from MYTABLE rr where
not (rr.jdoc ?? 'somefiled')
and ((rr.jdoc->'crazyfiled'->>'doublecrazyfiled')<>'gotyou')
You can see the same MYTABLE is used 3 times. The thing is, I have to run the same query for different tables i.e the MYTABLE substituted.
So I am trying to find - if anything like below is possible -
SET TABLENAME=CUS_DELTA --//then use the above like -
select * from $TABLENAME;
I am using postgres 13.5 with DBeaver for running the queries.
If not SQL, does DBeaver provide any such means.
If SQL can not support it, I am ok to use Dynamic SQL / PL SQL (though i have not idea about these) - if its not going to be too complicate for the above case. But I am not aware about the code, so request to share the same through an answer.

Answer 1

Read this article about Dynamic SQL carefully. Example from the docs:
EXEC SQL BEGIN DECLARE SECTION;
const char *stmt = "INSERT INTO test1 VALUES(?, ?);";
EXEC SQL END DECLARE SECTION;
EXEC SQL PREPARE mystmt FROM :stmt;
...
EXEC SQL EXECUTE mystmt USING 42, 'foobar';
Basically this way you can simply pass values. Now, your values are dynamic as well, but no worries. Declare your tablename as varchar and SELECT tbname INTO yourvariable FROM sometable. Then you can pass this variable to your dynamic query.
EDIT:
Minimalistic example:
Setting a variable to hard-coded value
SET TABLENAME = 'CUS_DELTA';
Setting a variable to a dynamic table name
SELECT tbname
INTO TABLENAME
FROM yourtable
And then let's use our TABLENAME variable like this:
EXEC SQL BEGIN DECLARE SECTION;
const char *stmt = "SELECT * FROM ?";
EXEC SQL END DECLARE SECTION;
EXEC SQL PREPARE mystmt FROM :stmt;
EXEC SQL EXECUTE mystmt USING TABLENAME;
The above is untested.