Question - View with a join based on two unequal strings.

Question

Hello -
First my apologies for the likely novice question.
I'm creating a view based on two tables as such:
SELECT *
FROM table1 LEFT OUTER JOIN table2 ON table1.string = table2.string AND table1.number = table2.number
Problem: table1.string looks like "A00A01%%%" and table2.string looks like "A1" (which would correspond to "A00A01%%%".
Question: Can I create the join based on the 4th and 6th character of the string = the other string, or should I create a view with a formula creating a new field and then create a second view? (Note: creating or changing the field in the original table is not an option).
Thank you.

Answer 1

Hi,
Yes, you can do that. Join conditions don't have to be as simple as "ON a.col1 = b.col2"; they can involve functions, like CONCAT and SUBSTR.
For example:
FROM            table1
LEFT OUTER JOIN table2
ON              SUBSTR (table1.string, 4, 1)
                ||
                SUBSTR (table1.string, 6, 1) = table2.string
...The query might be faster if you create a function-based index on the join condition from table1. This does not require changing table1 itself. (For a LEFT OUTER JOIN, like this, it probably won't matter.)