function keyToASTChild(key, namespace) {
  if (typeof key === 'string') {
    return columnToASTChild(key, namespace)
  }
  if (Array.isArray(key)) {
    const clumsyName = toClumsyName(key)
    return {
      type: 'composite',
      name: key,
      fieldName: clumsyName,
      as: namespace.generate('column', clumsyName)
    }
  }
}