使用单个查询更新SQL

Question

This question is asked by my friend. He faced this question during an interview. Please forget about db structure :), I think they asked this question to check logic :)

Here is the scenario. There is a hotel with different floors and different room numbers in each room.

Initially table will be like this;

Floor Rooms
1
1
1
2
2

Rooms column will have null values

We need to fill as shown below using a single query. Is this possible? If so how we can do that. Please advice.

Floor    Rooms
1        101
1        102  
1        103
2        201
2        202

Answer 1

Very simple,Code for SQL Server,

with cte as
(
select * 
,ROW_NUMBER() over (partition by  fno order by fno) as rowNo
 from hotel
 )
 update cte set rNo = fno*100 + rowNo

DEMO

Code of MySQL, I was able to select only, for update Temp table should be used, I am new to MYSQL.

set @type = 1;
set @num  = 0;

select fno,(fno*100) + row_number as newRommNo  from
(
select * 
,@num := if(@type = fno, @num + 1, 1) as row_number
,@type :=fno
 from hotel
) as a

DEMO OF MYSQL

Answer 2

试试这个

update tablename set `Rooms`=(Floor*100)+1

Answer 3

This is may be help for you

we must declare scalar variable:

SELECT fno, CASE WHEN fno = 1 THEN fno * 100 +@rooms :=@rooms + 1 
WHEN fno = 2 THEN fno * 100 +@room :=@room + 1 END FROM hotel, 
(SELECT @rooms := 0) AS w1, (SELECT @room := 0) AS w2

here demo : http://sqlfiddle.com/#!2/54c0d/1

Answer 4

Use this query if you're looking for a true atomic solution without having to set and reset session variables outside of your update query:

UPDATE floor_rooms
    INNER JOIN (
        SELECT DISTINCT floor, (@room := 0), (@floor := 0)
            FROM floor_rooms
            WHERE ISNULL(room)
    ) AS floors
    ON floor_rooms.floor = floors.floor
    SET floor_rooms.room =
        IF(@floor = floor_rooms.floor, @room := (@room + 1), @room := 1)
        + (@floor := floor_rooms.floor) * 100;

DEMO @ SQL Fiddle