Problems in using CLOB field

Question

I am trying to use a clob field in a select statment and I am getting "Ora-00932: inconsistent datatypes" error.
I am using Oracle 817.
Any idea or fix?

Answer 1

The reason your statement throws an error is because
of the DISTINCT, not because of joins. Oracle can
only do distinct on basic data types (CHAR, VARCHAR2,
NUMBER and DATE). It tries to do an implicit
conversion from CLOB to VARCHAR to do the DISTINCT.
CLOBS over 4000 characters cannot be converted to
VARCHAR2. So, even without any joins ...Agreed ... but my DISTINCT wasn't on the CLOB. It was on a VARCHAR2. Let me restate (hopefully a little more clearly) what I was referring too to see if you can think of any ways to do what I'm trying to do. The first example I know will work provided the CLOB doesn't contain over 4000 characters. The 2nd example (the same as the example originally mentioned) will not work. I'm wanting to do something like the 2nd example but with the same results as the first.
EX #1: (will work)
SELECT
DISTINCT table1.varcharField1,
table1.varcharField2,
table2.varcharField3,
DBMS_LOB.SUBSTR(table1.CLOBField4,DBMS_LOB.GETLENGTH(table1.CLOBField4)),
table3.varcharField5
FROM
table1,
table2,
table3
WHERE
table1.varcharField1 = table2.varcharField1
AND table1.varcharField1 = table3.varcharField1
AND table1.varcharField2 = 'XYZ'
EX #2: (will not work)
SELECT
DISTINCT table1.varcharField1,
table1.varcharField2,
table2.varcharField3,
table1.CLOBField4,
table3.varcharField5
FROM
table1,
table2,
table3
WHERE
table1.varcharField1 = table2.varcharField1
AND table1.varcharField1 = table3.varcharField1
AND table1.varcharField2 = 'XYZ'
This is SQL for a report so the entire contents of the CLOB field are required. (In actuality, the dbase column should have originally been defined as a VARCHAR2. Since we already have other programs in place that hit these table fields, we can't arbitrarily go back and change it.) If we leave the first SQL example in place, it'll work but it'll cause the SQL to crash if the data in that field ever exceeds 4000 characters. That's why we're trying to do away with the DBMS_LOB.SUBSTR() method. BUT if we don't interpret the CLOB in some other fashion, it'll throw the ORA-00932 error because of a data inconsistencies.
Any advice you could offer would certainly be appreciated.
BJ