数据分组取第一条高效率

查询中用到'IN'的地方，尽量用inner join

数据库分组取第一条

SELECT a.OrderNo, a.EquipNo FROM
(SELECT *, row_number () OVER (
        partition BY EquipNo,OrderNo //以某字段分组
        ORDER BY    
            CreateTime DESC
    ) AS [rowIndex] FROM Product_FeedBack WHERE BillType = 0 AND RelationNo IS NULL  )a
WHERE a.rowIndex = 1

也可以根据分组取某字段的最大值/最小值

SELECT   RetailerID, MAX (CreateTime) AS CreateTime
FROM  App_WarrantyCard   GROUP BY  RetailerID
ORDER BY  CreateTime