How to fix PL/SQL: ORA-00918: column ambiguously defined in Oracle - sql

Question

I'm creating a package in Oracle, and when I've compiled the body of the package, i am getting the PL/SQL: ORA-00918: column ambiguously defined error.
I've gone through the code, and double checked the aliases, so am a bit stumped as to why I am receiving this error.
The error in question is on Line 10.
The PERSON_CODE, FUND_YEAR and UIO_ID in the WHERE clause are the arguments on the function that I am creating in the package.
SELECT CASE
WHEN LH.PROP_NOT_TAUGHT > 50 AND LA.DELIVERY_PROVIDER IS NOT NULL THEN TO_NUMBER(OU.UKPRN)
ELSE LA.UK_PROV_NO
END AS UKPRN_T
FROM FES.LEARNER_AIMS LA
JOIN FES.LEARNER_HE LH
ON LH.PERSON_CODE = LA.PERSON_CODE
AND LH.FUNDING_YEAR = LA.FUNDING_YEAR
LEFT JOIN FES.ORGANISATION_UNITS OU
ON OU.ORGANISATION_CODE = LA.DELIVERY_PROVIDER
WHERE LA.PERSON_CODE = PERSON_CODE
AND LA.FUNDING_YEAR = FUND_YEAR
AND LA.UIO_ID = UIO_ID;

Answer 1

Your function parameter name and the name of the field are clashing, creating a shadowing effect. You can prefix the name of the parameter with the function name to remove the ambiguity
AND LA.UIO_ID = MyfunctionName.UIO_ID;
Alternatively, rename the parameter to avoid such occurrences.

Answer 2

Its always good practice to use table alais with columns Names.
SELECT CASE
WHEN LH.PROP_NOT_TAUGHT > 50 AND LA.DELIVERY_PROVIDER IS NOT NULL THEN TO_NUMBER(OU.UKPRN)
ELSE LA.UK_PROV_NO
END AS UKPRN_T
FROM FES.LEARNER_AIMS LA
JOIN FES.LEARNER_HE LH
ON LH.PERSON_CODE = LA.PERSON_CODE
AND LH.FUNDING_YEAR = LA.FUNDING_YEAR
LEFT JOIN FES.ORGANISATION_UNITS OU
ON OU.ORGANISATION_CODE = LA.DELIVERY_PROVIDER
WHERE LA.PERSON_CODE = <tableAlaisForPersonCode>PERSON_CODE
AND LA.FUNDING_YEAR = <tableAlaisForFUND_YEAR>FUND_YEAR
AND LA.UIO_ID = <tableAlaisForUIO_ID>UIO_ID;

Answer 3

. The PERSON_CODE, FUND_YEAR and UIO_ID are the arguments on the function.
It is bad practice to use PL/SQL parameter names which are the same as column names. The compiler applies the nearest namespace check, which means in this case it tries to map PERSON_CODE to a table column. Aliasing is optional so it doesn't realise that you're trying to reference PL/SQL parameters.
Because you have more than one table with a column called PERSON_CODE you get the ORA-00918 error. Otherwise you would just have a query which returned all rows.
The better practice is to name parameters differently; the convention is to prefix them with p_:
WHERE LA.PERSON_CODE = P_PERSON_CODE
AND LA.FUNDING_YEAR = P_FUND_YEAR
AND LA.UIO_ID = P_UIO_ID;

Answer 4

Alias is missing for the column UIO_ID, just provide OU.UIO_ID
SELECT CASE
WHEN LH.PROP_NOT_TAUGHT > 50 AND LA.DELIVERY_PROVIDER IS NOT NULL THEN TO_NUMBER(OU.UKPRN)
ELSE LA.UK_PROV_NO
END AS UKPRN_T
FROM FES.LEARNER_AIMS LA
JOIN FES.LEARNER_HE LH
ON LH.PERSON_CODE = LA.PERSON_CODE
AND LH.FUNDING_YEAR = LA.FUNDING_YEAR
LEFT JOIN FES.ORGANISATION_UNITS OU
ON OU.ORGANISATION_CODE = LA.DELIVERY_PROVIDER
WHERE LA.PERSON_CODE = PERSON_CODE
AND LA.FUNDING_YEAR = FUND_YEAR
AND LA.UIO_ID = OU.UIO_ID;