fix: one more error throw in case of table targeting not working

pgbelt/util/postgres.py

@@ -97,10 +97,16 @@ async def compare_data(
     dst_old_extra_float_digits = await dst_pool.fetchval("SHOW extra_float_digits;")
     await dst_pool.execute("SET extra_float_digits TO 0;")
 
+    has_run = False
     for table in set(pkeys):
-        # If specific table list is defined and iterated table is not in that list, skip.
-        if tables and (table not in tables):
+        # If specific table list is defined and the iterated table is not in that list, skip.
+        # Note that the pkeys tables returned from Postgres are all lowercased, so we need to
+        # map the passed conf tables to lowercase.
+        if tables and (table not in list(map(str.lower, tables))):
             continue
+
+        has_run = True  # If this runs, we have at least one table to compare. We will use this flag to throw an error if no tables are found.
+
         full_table_name = f"{schema}.{table}"
 
         logger.debug(f"Validating table {full_table_name}...")
@@ -171,6 +177,13 @@ async def compare_data(
                     f"Dest Row: {dst_row}"
                 )
 
+    # Just a paranoia check. If this throws, then it's possible pgbelt didn't migrate any data.
+    # This was found in issue #420, and previous commands threw errors before this issue could arise.
+    if not has_run:
+        raise ValueError(
+            "No tables were found to compare. Please reach out to the pgbelt for help, and check if your data was migrated."
+        )
+
     await src_pool.execute(f"SET extra_float_digits TO {src_old_extra_float_digits};")
     await dst_pool.execute(f"SET extra_float_digits TO {dst_old_extra_float_digits};")
     logger.info(