PG :: InvalidColumnReference：错误：用于Ruby on Rails应用程序中的SELECT DISTINCT

Question

我有一个如下所示的查询：

 Person.where.not(first_name: nil).where.not("lower(first_name)  = ?", 'mike').order('RANDOM()').limit(6).pluck("distinct(lower(first_name))")

当我尝试运行它时，它返回以下错误：

ActiveRecord::StatementInvalid: PG::InvalidColumnReference: ERROR:  for SELECT DISTINCT, ORDER BY expressions must appear in select list
LINE 1: ...AND (NOT (lower(first_name)  = 'mike'))  ORDER BY RANDOM() L...

我该如何解决这个问题？

Answer 1

Person.where.not(first_name: nil).where.not("lower(first_name)  = ?", 'mike').order('RANDOM()').limit(6).select("lower(first_name)").uniq

因为pluck会触发额外的查询，所以不应该使用select