DO $$
DECLARE
  current_default text;
BEGIN
  SELECT pg_catalog.pg_get_expr(d.adbin, d.adrelid)
    INTO current_default
  FROM pg_attribute a
  JOIN pg_class t ON t.oid = a.attrelid
  JOIN pg_namespace n ON n.oid = t.relnamespace
  LEFT JOIN pg_attrdef d ON d.adrelid = a.attrelid AND d.adnum = a.attnum
  WHERE n.nspname = '{{.SchemaName}}'
    AND t.relname = '{{.TableName}}'
    AND a.attname = '{{.ColumnName}}'
    AND a.attnum > 0
    AND NOT a.attisdropped;

{{- if .SetDefault }}
  IF current_default IS DISTINCT FROM {{quote .DefaultValue}} THEN
    ALTER TABLE {{qual_table .SchemaName .TableName}}
      ALTER COLUMN {{quote_ident .ColumnName}} SET DEFAULT {{.DefaultValue}};
  END IF;
{{- else }}
  IF current_default IS NOT NULL THEN
    ALTER TABLE {{qual_table .SchemaName .TableName}}
      ALTER COLUMN {{quote_ident .ColumnName}} DROP DEFAULT;
  END IF;
{{- end }}
END;
$$;