1、postgresql 查询每组第一个

　　　ROW_NUMBER () OVER (partition by 字段 ORDER BY  字段  DESC)

写法：SELECT  ROW_NUMBER () OVER (partition by 字段  ORDER BY  字段  DESC) AS  字段别名  FROM  表名；

　　　SELECT * FROM (SELECT *,ROW_NUMBER () OVER (partition by 字段  ORDER BY  字段  DESC) AS  字段别名(group_idx)  FROM  表名) AA WHERE AA.group_idx='1'

2、postgresql 查询加序号

　　　ROW_NUMBER () OVER (ORDER BY  字段  DESC)

写法：SELECT  ROW_NUMBER () OVER (ORDER BY  字段  DESC) AS  字段别名  FROM  表名