How do I copy data from one child table to another?

Short answer: Create an integration with an Update an item action on the same process. Set the source table for the target table and map each column. Every row is copied.

Why it happens

There's no built-in way to copy rows between two child tables on a form. An integration can do it, because the Update an item action can fill a table from another table's rows.

How to fix it

1. Create an integration with the trigger that fits your case.
2. Add the Kissflow Process action Update an item on the same process.
3. Set Table A (the source) as the source for Table B (the target).
4. Map each Table B field to the matching Table A field. Don't map the row _id. Every row is copied.
5. Test, then turn on the integration.

Updating rows directly with Update an item, rather than looping over them, also helps avoid concurrency issues. See the integration best practices.

If you want to combine two tables into one

1. Add two Update an item actions, one for each source table.
2. On the second action, use the filter to copy only unique values and skip duplicates.