How to resolve Oracle error ORA-01790?

Question

I have two select statements joined by "union". While executing that statement I've got:

Error report: SQL Error: ORA-01790: expression must have same datatype as corresponding expression 01790. 00000 - "expression must have same datatype as corresponding expression"

Maybe you can give me an advise on how to diagnose this problem?

Answer 1

Without looking at your SQL, I would guess that you have columns being UNION'ed that have different data types.

Answer 2

Here's what found:

ORA-01790: expression must have same datatype as corresponding expression

Cause: A SELECT list item corresponds to a SELECT list item with a different datatype in another query of the same set expression.

Action: Check that all corresponding SELECT list items have the same datatypes. Use the TO_NUMBER, TO_CHAR, and TO_DATE functions to do explicit data conversions.

I haven't seen your query, but I am guessing that one select in your union is not selecting the same columns as the other.

Answer 3

You need to make sure that corresponding columns in your union have the same data type. The easiest way would be to comment out columns one by one to narrow down to the column and then use explicit type conversion function in one of them to make types match.

Answer 4

The error is telling you that you're union-ing columns with different datatypes. There are oracle functions that will convert one type to another (e.g. "to_char"), you'll have to convert the datatypes into a common format, or at least one into the other. If you post the actual query/types it'd be possible to be more specifc.

Answer 5

You tried to execute a SELECT statement (probably a UNION or a UNION ALL), and all of the queries did not contain matching data types in the result columns.

Techonthenet - ORA-01790

Answer 6

As I mention in the question I'd like to have SUGGESTIONS for how to troubleshoot my problem. What I've done is enabled one column at a time in each select statement and found that I had mismatch at the very last column of my SQL UNION. Thanks a lot for participating and helping me, but I knew I had type mismatch, WHAT I didn't know is how to troubleshoot.