Update multiple rows by values taken from another table - tsql

Question

Here is what I could master so far:
declare #i int = 7;
declare #lat float;
declare #lng float;
declare #point ???; -- what type?
declare #location table(lat float, lng float)
insert #location values (32.097218, 34.770438199999944)
insert #location values (32.083847, 34.775618)
insert #location values (32.1600788, 34.771902)
insert #location values (31.9914283, 34.80780099999993)
insert #location values (32.1574281, 34.775191800000016)
insert #location values (29.5543212, 34.89448429999993)
insert #location values (32.8018919, 34.96268420000001)
while #i > 0
begin
-- this is a wrong way to do it
set #point = (select top (1) * from #location);
-- must set #lat and #lng here somehow, based on the
-- one row selected above. Deleting here is not
-- mandatory, but may be used, if needed.
delete top (1) from #location;
update top (1) rest_tbl
set lat = #lat, lng = #lng
where lat is null and private_label_id = 3
set #i = #i - 1
end;
Please don't mind the part, where I'm creating the #location variable - in the real world, it is an actual table, I'm just using it for PoC.

Answer 1

I think this is what you need. If you are on sql-server 2005 or above you could use CTE and row_number() function as below without a loop. Please replace cols_that_decides_order with correct column(s) to get the top records.
Also I think your lng will be rounded up when converting to float (ex; 34.770438199999944 >> 34.7704382).
--Declare the table with auto incremented identity with seed=7 and increment = -1.
declare #location table(mykey int identity(7,-1), lat float, lng float)
insert #location values (32.097218, 34.770438199999944)
,(32.083847, 34.775618)
,(32.1600788, 34.771902)
,(31.9914283, 34.80780099999993)
,(32.1574281, 34.775191800000016)
,(29.5543212, 34.89448429999993)
,(32.8018919, 34.96268420000001)
;with cte as (
select lat,lng, row_number() over (order by cols_that_decides_order) rn
from rest_tbl
where lat is null and private_label_id = 3
)
update c set c.lat = t.lat, c.lng = t.lng
from cte c join #location t on c.rn = t.myKey

Answer 2

I think Using Cursor in this matter will help
DECLARE db_cursor CURSOR FOR (Select lat,lng from #location
where lat not in (Select lat from rest_tbl where lat is not null));
DECLARE #lat Float;
DECLARE #lng Float;
OPEN db_cursor;
FETCH NEXT FROM db_cursor INTO #lat,#lng;
WHILE ##FETCH_STATUS = 0
BEGIN
UPDATE top (1) rest_tbl
SET lat =#lat,lng =#lng
where lat is null
FETCH NEXT FROM db_cursor INTO #lat,#lng;
END;
CLOSE db_cursor;
Delete from #location
where lat in (Select lat from rest_tbl where lat is not null)