如何删除mysql数据库中的重复记录？

Question

使用rails或mysql查询删除mysql数据库中重复记录的最佳方法是什么？

Answer 1

您可以做的是通过以下方式将不同记录复制到新表中:

 select distinct * into NewTable from MyTable

Answer 2

这是另一种没有特定语言的想法:

rs = `select a, b, count(*) as c from entries group by 1, 2 having c > 1`
rs.each do |a, b, c|
  `delete from entries where a=#{a} and b=#{b} limit #{c - 1}`
end

编辑:

荣誉对奥拉夫为"具有"提示:)

Answer 3

好吧,如果它是一个小桌子,你可以从rails控制台做

class ActiveRecord::Base
  def non_id_attributes
    atts = self.attributes
    atts.delete('id')
    atts
  end
end

duplicate_groups = YourClass.find(:all).group_by { |element| element.non_id_attributes }.select{ |gr| gr.last.size > 1 }
redundant_elements = duplicate_groups.map { |group| group.last - [group.last.first] }.flatten
redundant_elements.each(&:destroy)

Answer 4

检查重复条目:

SELECT DISTINCT(req_field) AS field, COUNT(req_field) AS fieldCount FROM 
table_name GROUP BY req_field HAVING fieldCount > 1

删除重复查询:

DELETE FROM table_name 
USING table_name, table_name AS vtable 
WHERE 
    (table_name.id > vtable.id) 
AND (table_name.req_field=req_field)

替换req_field和table_name - 应该没有任何问题.