Sql-server – SQL update multiple rows in destination table with same id but different values from source table

sql serversql-server-2008-r2update

I have two different tables with a common column called id:

Table1
----  -------
id  |  Date
----  -------
1      null
1      null
2      null
2      null
2      null
2      null
3      null
4      null
4      null

Table2
----  -------
id  |  Date
----  -------
1      2013-01-29 08:50:00.000
1      2013-01-29 15:28:00.000
2      2013-01-31 11:56:00.000
2      2013-03-11 16:08:00.000
2      2013-01-31 14:04:00.000
2      2013-01-31 14:08:00.000
3      2013-02-28 23:44:00.000
4      2013-01-31 14:04:00.000
4      2013-01-31 14:08:00.000

I need to write an update statement that will basically put the value of the first row with id=1 from Table2 into Table1 with an id=1 and the second row with id=1 from Table2 into Table1 with an id=1 so that Table1 now looks like this

Table1
----  -------
id  |  Date
----  -------
1      2013-01-29 08:50:00.000
1      2013-01-29 15:28:00.000

Currently this SQL statement

UPDATE Table1
  SET Table1.date = T2.date
  FROM 
  Table2 T2
  INNER JOIN Table1 T1
  ON T1.date = T2.date

is making Table1 look like this, where it applies the first date it finds for that id to all the rows with matching ids in the destination table

Table2
----  -------
id  |  Date
----  -------
1      2013-01-29 08:50:00.000
1      2013-01-29 08:50:00.000

Is there a way to udpate Table1 to look like this below:

Table1
----  -------
id  |  Date
----  -------
1      2013-01-29 08:50:00.000
1      2013-01-29 15:28:00.000
2      2013-01-31 11:56:00.000
2      2013-03-11 16:08:00.000
2      2013-01-31 14:04:00.000
2      2013-01-31 14:08:00.000
3      2013-02-28 23:44:00.000
4      2013-01-31 14:04:00.000
4      2013-01-31 14:08:00.000

Is there a way to do this in a SQL statement? I don't want to use a cursor preferably.

There are other columns in both the tables and not all id values in Table1 might be there in Table2 and vice versa. Those other rows and columns I don't want to touch or alter.

Best Answer

Couldn't find a SQL Server 2008 fiddle engine so I had to opt for a SQL Server 2014 ... so not sure if the following will work in SQL Server 2008, but fwiw ...

Setup some sample data:

create table Table1(id int, Date datetime null);
create table Table2(id int, Date datetime);

insert Table1 values (1,null)
insert Table1 values (1,null)
insert Table1 values (2,null)
insert Table1 values (2,null)
insert Table1 values (2,null);

insert Table2 values (1,'2013-01-29 08:50:00.000')
insert Table2 values (1,'2013-01-29 15:28:00.000')
insert Table2 values (2,'2013-01-31 11:56:00.000')
insert Table2 values (2,'2013-03-11 16:08:00.000')
insert Table2 values (2,'2013-01-31 14:04:00.000');

Keeping in mind that we haven't been provided (yet) with any means to determine which rows to match between Table1 and Table2 for a given id value, I'll just let row_number() generate a 'matching' rowid.

And then we'll make use of SQL Server's ability to update Table1 via a derived table definition:

update T1 
set    T1.Date=T2.Date

from   (select row_number() over(partition by id order by Date) as rowid,
               id,
               Date
        from   Table1 
        where  Date is NULL) T1

join   (select row_number() over(partition by id order by Date) as rowid,
               id,
               Date
        from   Table2) T2

on      T1.id    = T2.id
and     T1.rowid = T2.rowid;

And the results:

select * from Table1;

id  Date
--- --------------------
1   2013-01-29T08:50:00Z
1   2013-01-29T15:28:00Z
2   2013-01-31T11:56:00Z
2   2013-01-31T14:04:00Z
2   2013-03-11T16:08:00Z

And here's a SQL Fiddle for the above.

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