joining wide tables (10s of unique cols) - sql

Question

I have multiples tables which need to be joined on multiple common attributes such the different attributes can be shown in a single table.
table1
+--------+---------+-------+
| make | model | r_yr |
+--------+---------+-------+
| toyota | corolla | 1999 |
| toyota | camry | 2002 |
| toyota | qualis | 2004 |
| toyota | rav4 | 2006 |
+--------+---------+-------+
table2
+--------+---------+--------+
| make | model | kms |
+--------+---------+--------+
| toyota | corolla | 25000 |
| toyota | camry | 50000 |
+--------+---------+--------+
table4
+--------+---------+---------+
| make | model | mileage |
+--------+---------+---------+
| toyota | corolla | 20 |
| toyota | qualis | 25 |
+--------+---------+---------+
table5
+--------+----------+-------+
| make | model | colr |
+--------+----------+-------+
| toyota | camry | blue |
| toyota | rav4 | green |
+--------+----------+-------+
I'm doing the following to join the results
select a.make, a.model,a.r_yr,b.kms,c.mileage,d.colr
from table1 as a
left join table2 as b
on b.make=a.make and b.model=a.model and b.r_yr=a.r_yr
left join table3 as c
on c.make=a.make and c.model=a.model and c.r_yr=a.r_yr
left join table4 as d
on d.make=a.make and d.model=a.model and d.r_yr=a.r_yr
This gives a table like below
+--------+---------+-------+-------+----------+--------+
| make | model | r_yr | kms | mileage | colr |
+--------+---------+-------+-------+----------+--------+
| toyota | corolla | 1999 | 25000 | 20 | |
| toyota | camry | 2002 | 50000 | | blue |
| toyota | qualis | 2004 | | 25 | |
| toyota | rav4 | 2006 | | | green |
+--------+---------+-------+-------+----------+--------+
However the issue I have is that, for the real data set I'm working with, there are 5 common cols per table and around 20-40 unique attributes per table requiring to specify 20-40 col names in the query in the form of b.kms, ....,c.mileage, ......,d.colr,..... Is there a work around to not having to specify those unique columns by specifying all except the common cols or other ways ?

Answer 1

You cannot do something like SELECT all except x,y,z ...
But you can simplify this query using USING clause instead of JOIN ... ON
Demo: http://sqlfiddle.com/#!17/fa97a/6
select *
from table1 as a
left join table2 as b
USING (make, model)
left join table3 as c
USING (make, model)
left join table4 as d
USING (make, model)
| make | model | r_yr | kms | mileage | colr |
|--------|---------|------|--------|---------|--------|
| toyota | camry | 2002 | 50000 | (null) | blue |
| toyota | corolla | 1999 | 25000 | 20 | (null) |
| toyota | qualis | 2004 | (null) | 25 | (null) |
| toyota | rav4 | 2006 | (null) | (null) | green |
Note: In the above example I am using only two common columns (make, model) since in your example r_yr is not a common column because it is only in table1