SQL querying two sources - sql

Question

I have a View and Table as example below
Table1
+---------+------+
| Country | City |
+---------+------+
| UK | LDN |
| US | NEY |
| US | LAX |
+---------+------+
View1
+---------+---------+-------+
| Column1 | Column2 | Site |
+---------+---------+-------+
| Test | Test2 | UKLDN |
| Test | Test2 | USNEY |
| Test | Test2 | USLAX |
| Test | Test2 | PELMA |
+---------+---------+-------+
The result i'm trying to achieve is show all rows from View1, that have a View1.Site column matching Table1.Country and Table1.City. My confusion is how do to it as i'm not an sql person but more C# etc.
The resulting data I want to create is below. I don't know if I can do this solely from View1 or what functions to use.
Result
+---------+---------+-------+---------------+
| Column1 | Column2 | Site | ExistInTable1 |
+---------+---------+-------+---------------+
| Test | Test2 | UKLDN | Y |
| Test | Test2 | USNEY | Y |
| Test | Test2 | USLAX | Y |
| Test | Test2 | PELMA | N |
+---------+---------+-------+---------------+
Thanks

Answer 1

You can try this.
SELECT V.*, CASE WHEN T.Country IS NULL THEN 'N' ELSE 'Y' END ExistInTable1 FROM View1 V
LEFT JOIN Table1 T ON V.Site = (T.Country + T.City)

Answer 2

This is T-SQL, but the format should be very similar for most other flavors of SQL.
SQL Fiddle
MS SQL Server 2014 Schema Setup:
CREATE TABLE Table1 (Country varchar(5),City varchar(5)) ;
INSERT INTO Table1 (Country,City)
VALUES ( 'UK','LDN'),('US','NEY'),('US','LAX')
;
CREATE TABLE View1 (Column1 varchar(10), Column2 varchar(10), Site varchar(10)) ;
INSERT INTO View1 (Column1,Column2,Site)
VALUES ('Test','Test2','UKLDN')
, ('Test','Test2','USNEY')
, ('Test','Test2','USLAX')
, ('Test','Test2','PELMA')
;
Query 1:
SELECT v.Column1, v.Column2
, CASE WHEN LEN(COALESCE(t.Country,t.City)) > 0 THEN 'Y' ELSE 'N' END AS ExistsInTable1
FROM View1 v
LEFT OUTER JOIN Table1 t ON v.Site = (t.Country+t.City)
Results:
| Column1 | Column2 | ExistsInTable1 |
|---------|---------|----------------|
| Test | Test2 | Y |
| Test | Test2 | Y |
| Test | Test2 | Y |
| Test | Test2 | N |

Answer 3

You need to do a LEFT JOIN with your table and then check if it matches or not with the info from the view, like this:
SELECT
VW.Column1
,VW.Column2
,VW.Site
,CASE WHEN ISNULL(T.country, T.city) IS NULL THEN 'N' ELSE 'Y' END AS ExistInTable1
FROM View1 VW
LEFT JOIN Table1 T
ON VW.site = CONCAT(T.country, T.City)
The LEFT JOIN keyword returns all records from the left table (View1), and the matched records from the right table (Table1). The result is NULL from the right side, if there is no match.(check done with the CASE statement)
You can test it Here as well.