ORACLE PL/SQL Variable Function Scope - Need Explanation - sql

Question

I just tripped over an answer to a problem I was having with a PL/SQL variable not being recognized by a function and I was hoping someone could explain to me why my solution worked and what is happening "underneath the hood".
Background
As part of an optimization project, I am trying to collect metrics on individual SQL scripts within a Stored Procedure. The Stored Proc that I am dissecting has an In-type date parameter that I need to define in order to run each individual SQL Script:
CREATE OR REPLACE myStoredProc (DATE_IN DATE, ERROR_OUT OUT VARCHAR2)
IS
BEGIN
--Truncate Temp Tables
--6 Individual SQL Scripts
EXCEPTION
--Error Handling
END;
To run each script individually, I decided to just drop each SQL statement into a PL/SQL block and feed the DATE_IN parameter in as a variable:
DECLARE
DATE_IN DATE := TO_DATE('16-JUL-2014','DD-MON-RR');
BEGIN
--Place individual script here
END;
The Problem
This approach worked fine for a couple of the queries that referred to this DATE_IN variable but one query with a reference to an outside function which takes DATE_IN as a parameter started throwing an ORA-00904 error:
DECLARE
DATE_IN DATE := TO_DATE('16-JUL-2014','DD-MON-RR');
BEGIN
insert into temp_table
SELECT table1.field1,
table1.field2,
table2.fieldA,
MyFunction(table1.field1, DATE_IN) --This was the problem line
FROM
table1,
table2
WHERE EXISTS (inner query)
AND table1.keys = table2.keys
AND table2.date <= DATE_IN
END;
Solution
At the advice of another Developer, I was able to get around this error by adding a colon (:) in front of the DATE_IN variable that I was passing into the function so that the problem line read MyFunction(table1.field1, :DATE_IN). As soon as I did that, my error disappeared and I was able to run the query without issue.
I was happy for the result but the other Developer wasn't able to explain why it was needed, only that it was necessary to call any functions or other stored procs from a PL/SQL statement. I assume this has something to do with scope but I would like to get a better explanation as to why this colon was necessary for the function to see the variable.
Questions
I've tried to do a little research looking over Oracle documentation on parameters, variables, binding/declaring and constants but my research has only given me more questions:
After reading up on variables, I now question if that is the correct term for what I have been using (since I didn't actually use the VARIABLE command and I'm passing in a date - which is not an allowable data type). If my DATE_IN DATE := statement is not a variable, then what is it?
Why were the rest of my references to DATE_IN recognized by the compiler but passing the value to the function was out of scope?
What exactly is the colon (:) doing here? Is this turning that into a bind variable?
Thanks in advance. I appreciate any guidance you can provide!
----------------------------------EDIT--------------------------------------
I was asked to provide additional information. My Db version is 11G, 11.2.0.2.0. The query that I was able to reproduce this error is below.
DECLARE
EXTRACT_DT_IN DATE := TO_DATE('16-JUL-2014','DD-MON-RR');
BEGIN
--This begins the pre-optimized query that I'm testing
insert into AELI_COV_TMP_2_OPT
SELECT /*+ ordered use_nl(CM MAMT) INDEX (CM CSMB_CSMB2_UK) INDEX (MAMT (MBAM_CSMB_FK_I) */
CM.CASE_MBR_KEY
,CM.pyrl_no
,MAMT.AMT
,MAMT.FREQ_CD
,MAMT.HOURS
,aeli$cov_pdtodt(CM.CASE_MBR_KEY, EXTRACT_DT_IN)
FROM
CASE_MEMBERS CM
,MEMBER_AMOUNTS MAMT
WHERE EXISTS (select /*+ INDEX(SDEF SLRY_BCAT_FK_I) */
'x'
from SALARY_DEF SDEF
where SDEF.CASE_KEY = CM.CASE_KEY
AND SDEF.TYP_CD = '04'
AND SDEF.SLRY_KEY = MAMT.SLRY_KEY)
AND CM.CASE_MBR_KEY = MAMT.CASE_MBR_KEY
AND MAMT.STAT_CD = '00'
AND (MAMT.xpir_dt is null or MAMT.xpir_dt > EXTRACT_DT_IN)
AND MAMT.eff_dt <= EXTRACT_DT_IN;
--This ends the pre-optimized query that I'm testing
END;
Here is the error I'm encountering when trying to run an Explain Plan on this statement. I am able to get past this error if I remove reference to line 13 or I add a colon (:) to the EXTRACT_DT_IN on that line.
----------------------EDIT 2-------------------
Here is the function signature of aeli$.cov_pdtodt. (I've replaced the owner for security reasons).
CREATE OR REPLACE function __owner__.aeli$cov_pdtodt
(CASE_MBR_KEY_IN IN NUMBER, EXTRACT_EFF_DT_IN DATE)
RETURN DATE IS
PDTODT DATE;

Answer 1

Your anonymous block is fine as it is, as long as you execute the whole block. If you try to execute just the insert, or its select, as a standalone command then it will indeed fail with ORA-00904.
That isn't quite a scope problem, it's a context problem. You're trying to refer to a PL/SQL variable in an SQL context, and that is never going to work.
In a PL/SQL context this would work:
declare
some_var dual.dummy%type := 'X';
begin
insert into some_table
select dummy from dual where dummy = some_var;
end;
/
... because the insert has access to the PL/SQL some_var.
In an SQL context this will error:
select * from dual where dummy = some_var;
... because it's looking for a column called SOME_VAR, and there isn't one.
If you do this instead:
select * from dual where dummy = :some_var;
... the some_var is now a client-managed bind variable. If you execute that you'll either be prompted for the bind value, or given a not-all-variables-bound error, or bind-variable-not-declared, or similar, depending on your client.
If you only do an explain plan of that though, e.g. with
set auto trace traceonly explain
select * from dual where dummy = :some_var;
... then the bind variable doesn't necessarily have to be populated for the plan to be calculated. Some clients may still complain and want a bind value, but the parser would be OK with it - enough to produce a plan anyway. Though not able to take advantage of bind variable peeking or histograms etc.
For example, SQL Developer happily produces a plan for your original sample query if both references are turned into bind variables, just the insert ... part of the block is selected, and you press Explain Plan (F10).

Answer 2

I'm not sure what you read, but you're mixed up on a few things here.
Your DATE_IN is a variable. You don't need to type 'VARIABLE' anywhere to declare a variable, all you need is the name of the variable and the datatype.
All of the below are legitimate variables in PL/SQL (although poorly named).
variable_1 NUMBER;
variable_2 VARCHAR2(100);
variable_3 DATE;
It's hard to tell what you're doing in your code without seeing it all. Do you have two DATE_IN variables declared within the same block? Is DATE_IN the name of a column in your table?
If you have a column named DATE_IN in table1 or table2, that's likely your problem. Oracle doesn't know if you want to use your variable or your column, and it will always default to the column name. Your function would be expecting a DATE and receiving a column, hence the error.