DO {{dollar_delimiter}}
DECLARE
  current_not_null boolean;
BEGIN
  SELECT a.attnotnull
    INTO current_not_null
  FROM pg_attribute a
  JOIN pg_class t ON t.oid = a.attrelid
  JOIN pg_namespace n ON n.oid = t.relnamespace
  WHERE n.nspname = {{quote .SchemaName}}
    AND t.relname = {{quote .TableName}}
    AND a.attname = {{quote .ColumnName}}
    AND a.attnum > 0
    AND NOT a.attisdropped;

  IF current_not_null IS NOT NULL AND current_not_null IS DISTINCT FROM {{.NotNull}} THEN
{{- if .NotNull }}
    ALTER TABLE {{qual_table .SchemaName .TableName}}
      ALTER COLUMN {{quote_ident .ColumnName}} SET NOT NULL;
{{- else }}
    ALTER TABLE {{qual_table .SchemaName .TableName}}
      ALTER COLUMN {{quote_ident .ColumnName}} DROP NOT NULL;
{{- end }}
  END IF;
END;
{{dollar_delimiter}};