SQL 查询查找每个客户的第一条记录并更新

Question

我有一个 table，其中有两列，即客户，project_id。我的要求是为每个客户找到第一个 project_id，并相应地命名例如 'General Project'，如果为客户找到了多个项目，则将下一个项目命名为 concat('PROJECT', '-', project_id)。在下图中，您可以看到第 4 列数据是我要求的结果，但我不确定如何找到它？提前致谢

Answer 1

您可以使用 row_number() 和字符串操作：

select t.*,
       (case when row_number() over (partition by customer order by row_number()) = 1
             then 'General Project'
             else replace('Project-[n]', '[n]', project_id) 
        end) as project_name
from t;

这恰好适用于 Oracle 和 SQL 服务器。

Answer 2

这是一个选项（在 Oracle 中有效；无法说明 SQL 服务器）。示例数据（您已经拥有并且不输入它位于第 1 - 13 行。您可能感兴趣的查询从第 15 行开始。

SQL> with
  2  test (row_num, customer, project_Id) as
  3    -- sample data
  4    (select 1, 115432, 1 from dual union all
  5     select 2, 115432, 2 from dual union all
  6     select 3, 115432, 3 from dual union all
  7     --
  8     select 4, 116500, 1 from dual union all
  9     select 5, 116500, 2 from dual union all
 10     --
 11     select 6, 112342, 3 from dual union all
 12     select 7, 112342, 4 from dual
 13    ),
 14  --
 15  data as
 16    (select row_num, customer, project_id,
 17            row_number() over (partition by customer order by project_id) rn
 18     from test
 19    )
 20  -- final query
 21  select row_num, customer, project_id,
 22    --
 23    case when rn = 1 then 'GENERAL PROJECT'
 24         else 'PROJECT-' || project_id
 25    end as project_name
 26  from data
 27  order by row_Num;

   ROW_NUM   CUSTOMER PROJECT_ID PROJECT_NAME
---------- ---------- ---------- -------------------------
         1     115432          1 GENERAL PROJECT
         2     115432          2 PROJECT-2
         3     115432          3 PROJECT-3
         4     116500          1 GENERAL PROJECT
         5     116500          2 PROJECT-2
         6     112342          3 GENERAL PROJECT
         7     112342          4 PROJECT-4

7 rows selected.

Answer 3

如果第一个项目编号总是小于其他项目那么你可以尝试：

select customer,project_id,
    case when project_id=(select min(project_id) from table t2 where 
    t.customer=t2.customer) then 'General Project'
    else concat('Project-',project_id)
    end Project_Name
from table t ;

这适用于 mysql。

SQL 查询查找每个客户的第一条记录并更新

SQL query to find first record of each customer and update

sql

rank

dense-rank

sql-server-2012