SQL Server connecting several Selects - sql

Question

I have the following statement:
Select No, Region = 'Ohio'
FROM table
where PostCode >='0001'
AND PostCode <= '4999'
which updates me the table with the correct state in the field Region. How can I expand that statement with several other WHERE conditions in the same statement?
e.g.
Region = 'NewYork'
Where PostCode >='5000'
AND PostCode <= '7999'
My solution would be to build several Statements, for each Region, but there must be a better way having them all in one.

Answer 1

Two common ways to select/set different values based on multiple criteria in a single query are case statements and doing a join on another table with those values. I should also point out that you can take advantage of the between operator in SQL server for much of this.
CASE statements in a single query
A case statement might be useful if you have a small set of criteria, or if you just need to throw together an adhoc query. Here is an example of using a case statement:
select
No,
Region = case
when (PostCode >= '0001' and PostCode <= '4999')
'Ohio'
when (PostCode between '5000' and '7999')
'NewYork'
else
'Unknown'
end
from [...]
JOIN a table with the values and criteria
This is definitely the better method for something like evaluating 50 states - especially since this data is likely static. The idea is that you will want to have a table that contains the criteria and the value, and then join it to the table.
Here is an example using a temp table - you would likely want to use a real table for something as common as states.
-- Setup a #states table
create table #states (state varchar(20), PostCodeMin char(4), PostCodeMax char(4))
insert into #states values ('Ohio', '0001', '4999')
insert into #states values ('NewYork', '5000', '7999')
-- Now query it
select
t.No,
State = isnull(s.state, 'Unknown')
from
my_table t
left outer join #states s
on (t.PostCode between s.PostCodeMin and s.PostCodeMax)
Note that in the above query, I do a left outer join to #states, in case the state isn't setup. I also select the State using isnull, in case the outer join doesn't return anything for that particular row in my_table.

Answer 2

You can create a calculated field using a case statement on region. If there is going to be many "Unknown" records returned then you may want to tweak the WHERE clause to filter out nonessential records for better performance.
SELECT
*
FROM
(
Select
No,
Region =
CASE
WHEN PostCode >'0001' AND PostCode <='4999' THEN 'Ohio'
WHEN PostCode >'5000' AND PostCode <='7999' THEN 'New York'
ELSE
'Unknown'
END
FROM table
where PostCode >='0001' AND PostCode <= '7999'
)AS X
ORDER BY
Region