processDataTable example

// Add the schema for base field definitions.           elseif ($table_mapping->allowsSharedTableStorage($this->fieldStorageDefinitions[$field_name])) {
            $column_names = $table_mapping->getColumnNames($field_name);
            $storage_definition = $this->fieldStorageDefinitions[$field_name];
            $schema[$table_name] = array_merge_recursive($schema[$table_name], $this->getSharedTableFieldSchema($storage_definition, $table_name, $column_names));
          }
        }
      }

      // Process tables after having gathered field information.       if (isset($tables['data_table'])) {
        $this->processDataTable($entity_type, $schema[$tables['data_table']]);
      }
      if (isset($tables['revision_data_table'])) {
        $this->processRevisionDataTable($entity_type, $schema[$tables['revision_data_table']]);
      }

      // Add an index for the 'published' entity key.       if (is_subclass_of($entity_type->getClass(), EntityPublishedInterface::class)) {
        $published_key = $entity_type->getKey('published');
        if ($published_key
            && isset($this->fieldStorageDefinitions[$published_key])
            && !$this->fieldStorageDefinitions[$published_key]->hasCustomStorage()) {