Question

I have two tables and I’m selecting data from the first table. If the condition is meet(Alias type = 2) and the data in second table for the id from the first table exist the I want to select the column from the second table. Here is data to explain more:

Table 1

id | Name         | Location  
---+--------------+---------  
34 |John Smith    |NewYork  
36 |Mike Smith    |London  
45 |Bob Smith     |Los Angeles  

Table 2

id | Alias             | Alias type     
---+-------------------+-------  
36 |Warren Johnson     |1  
36 |William Williams   |2  

Wanted results if alias type = 2

id |Name               | Location   
---+-------------------+---------  
34 |John Smith         |NewYork  
36 |William Williams   |London  
45 |Bob Smith          |Los Angeles  

Can you help me write query to get the wanted results? Tell me if I need to explain more. I’m using a SQL Server database.

Answer 1

You can use a left outer join onto Table2, and then COALESCE the Alias and Name results like this:

SELECT Table1.ID, COALESCE(Table2.Alias, Table1.Name) AS Name, 
    Table1.Location
FROM Table1
LEFT OUTER JOIN Table2 ON Table1.ID = Table2.ID AND Table2.AliasType = 2

COALESCE works by finding the first non-null value in the supplied values.