Oracle SQL substitution variable, the scope of substitution - sql

Question

I have been pondering about what and how much I can actually put into the substitution variable. can we only have it to replace a single 'entity' but not a string of command? I found if I want to substitute a block of actual SQL, it did not work (in SqlDeveloper).
I wonder how I can get around this...
/*------test--------------*/
CREATE TABLE Test_Persons (
PersonID int,
LastName varchar(255),
FirstName varchar(255)
);
INSERT INTO Test_Persons
(PersonID,LastName,FirstName)
values(1,'LN_1','FN_1');
INSERT INTO Test_Persons
(PersonID,LastName,FirstName)
values(2,'LN_2','FN_2');
INSERT INTO Test_Persons
(PersonID,LastName,FirstName)
values(3,'LN_21','FN_2');
commit;
--------------sub-table, worked!---
set define #;
define first_name_input = 'FN_2';
define last_name_input = 'LN_2';
define tbl_Test_Persons = 'Test_Persons';
define temp_tbl_Test_Persons_FN = 'Test_Persons_FN';
with
#temp_tbl_Test_Persons_FN as
(
select * from #tbl_Test_Persons tp
where tp.FIRSTNAME = '#first_name_input'
)
select * from #temp_tbl_Test_Persons_FN tp
where tp.LASTNAME = '#last_name_input';
set define off;
--------------sub-table, replace the entire with clause, does NOT work - 'Invalid value for DEFINE command.'!---
set define #;
define first_name_input = 'FN_2';
define last_name_input = 'LN_2';
define tbl_Test_Persons = 'Test_Persons';
define temp_tbl_Test_Persons_FN = 'Test_Persons_FN2';
define with_clause = '
with
#temp_tbl_Test_Persons_FN as
(
select * from #tbl_Test_Persons tp
where tp.FIRSTNAME = ''#first_name_input''
)
';
#with_clause
select * from #temp_tbl_Test_Persons_FN tp
where tp.LASTNAME = '#last_name_input';
set define off;

Answer 1

From the documentation (for SQL*Plus but applies to SQL Developer too):
If the value of a defined variable extends over multiple lines (using the SQL*Plus command continuation character), SQL*Plus replaces each continuation character and carriage return with a space.
SQL Developer actually behaves slightly differently, and leaves the continuation character inside the string, which isn't helpful. But is also leaves the line breaks, so you can double-up the continuation character from - to --to stop it causing a problem, as that is then treated a comment; so you can do:
define with_clause = '--
with--
#temp_tbl_Test_Persons_FN as--
(--
select * from #tbl_Test_Persons tp--
where tp.FIRSTNAME = ''#first_name_input''--
)--
';
But there is a further complication, because #with_clause isn't recognised as a command - as you aren't yet in a command substitution doesn't happen. You can get around that, messily, with a subquery:
select * from (
#with_clause
select * from #temp_tbl_Test_Persons_FN tp
where tp.LASTNAME = '#last_name_input'
);
which isn't ideal. But if you do that, the script output window shows the substitution happening and you get a row back:
old:select * from (
#with_clause
select * from #temp_tbl_Test_Persons_FN tp
where tp.LASTNAME = '#last_name_input'
)
new:select * from (
--
with--
Test_Persons_FN2 as--
(--
select * from Test_Persons tp--
where tp.FIRSTNAME = 'FN_2'--
)--
select * from Test_Persons_FN2 tp
where tp.LASTNAME = 'LN_2'
)
PERSONID LASTNAME FIRSTNAME
---------- --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
2 LN_2 FN_2
(Also, interestingly, this still doesn't work in SQL*Plus if you use # as the substitution character - you get "ORA-24333: zero iteration count". It doesn't get that error with & though; I haven't tried any others. And you have to go back to a single concatenation character. But even with those changes it still doesn't substitute the with clause properly. Not sure why yet.)