Can you use SQL transct in SQLite ?
If not, other embedded databases exist and which ones have these functions?
Try to do full join in the following way, but do not allow it.
SELECT marbete.id_marbete, producto.sku, producto."desc", marbete.cantidad as "Cantidad marbete", inventario_teorico.cantidad as "Cantidad Inventario teorico"
FROM producto
FULL OUTER JOIN inventario_teorico ON inventario_teorico.id_producto = producto.id
FULL OUTER JOIN marbete ON marbete.id_producto = producto.id;'