What is the required condition about join columns when creating custom joins using user extension?

What is the required condition about join columns when creating custom joins using user extension?

• A. They must be of compatible data types
• B. They must be identical names
• C. They must be numeric
• D. They must be in the same table

Answer: (A)

When you set up a custom join through a user extension, the key idea is that the two columns you join on must be able to be compared meaningfully. That means their data types should be compatible. If you try to join a numeric column with a non-numeric one (for example, a number column to a text column), the database can’t reliably compare the values unless you cast them, which can introduce errors and slow things down. So ensuring data type compatibility allows the join to work cleanly and efficiently, possibly using indexes and standard equality or range comparisons. The names of the columns don’t have to be the same, and you can join on various data types as long as the types align or are safely compatible. You don’t have to join columns from the same table; joins usually relate columns from different tables. The essential condition is that the data types line up so the database can compare the values in the join predicate.

When you set up a custom join through a user extension, the key idea is that the two columns you join on must be able to be compared meaningfully. That means their data types should be compatible. If you try to join a numeric column with a non-numeric one (for example, a number column to a text column), the database can’t reliably compare the values unless you cast them, which can introduce errors and slow things down. So ensuring data type compatibility allows the join to work cleanly and efficiently, possibly using indexes and standard equality or range comparisons.

The names of the columns don’t have to be the same, and you can join on various data types as long as the types align or are safely compatible. You don’t have to join columns from the same table; joins usually relate columns from different tables. The essential condition is that the data types line up so the database can compare the values in the join predicate.