SQL Query Left Outer Join To Current Query - sql

Question

I have a query and I want to look up the values from other table as a reference but not mess up my current query results. I think I have to use a Outer Left Join, but not sure how to incorporate that with my current query.
My current query looks similar to this:
SELECT a.primary_key,
a.phase,
b.project_number,
c.LENGTH,
d.color
FROM TableA a,
TableB b,
TableC c,
TableD d
WHERE c.primary_key = a.PROJECT_ID
AND b.primary_key = a.PROJECT_ID
AND b.primary_key = d.project_ID
AND (c.date IS NULL OR c.number IS NULL)
AND d.color IN ('black','red','blue')
ORDER BY 1
Now, that gives me a table of 50 results. 'TableContacts' has the look up value to my b.project_number. So say my table of 50 results, only 10 of them have b.project_number, I need the lookup values from 'TableContacts' to also show in my results, but I don't want that to affect my results and cut it down to 10, I still need my original 50 results, just with that additional information. Help?

Answer 1

Just add the CONTACTS table to your joins:
SELECT a.primary_key,
a.phase,
b.project_number,
c.LENGTH,
d.color,
ct.lookup_value --<< this is from the CONTACTS table
FROM TableA a
JOIN TableB b ON b.primary_key = a.PROJECT_ID
JOIN TableC c ON c.primary_key = a.PROJECT_ID
JOIN TableD d ON b.primary_key = d.project_ID
LEFT JOIN contacts ct ON ct.some_column = b.project_Number --<< this is the outer join to the CONTACTS table
WHERE (c.date IS NULL OR c.number IS NULL)
AND d.color IN ('black','red','blue')
ORDER BY 1
As you obfuscated your table and column names it's hard to guess how exactly the join condition on the CONTACTS table should look like.

Answer 2

You could use this approach:
Create a table with the results of your current query:
create table t1 as
SELECT a.primary_key,
a.phase,
b.project_number,
c.LENGTH_col,
d.color
FROM a,b,c,d
WHERE c.primary_key = a.PROJECT_ID
AND b.primary_key = a.PROJECT_ID
AND b.primary_key = d.project_ID
AND (c.date_col IS NULL OR c.number_col IS NULL)
AND d.color IN ('black','red','blue')
ORDER BY 1;
Use a union to get the desired results:
select t1.primary_key, t1.phase, t1.project_number, t1.length_col, t1.color, TableContacts.lookup_column
from t1, TableContacts
where t1.project_number = TableContacts.project_number
UNION
select t1.primary_key, t1.phase, t1.project_number, t1.length_col, t1.color, null
from t1 where t1.project_number is null;
Illustration by creating dummy data:
select * from a;
PRIMARY_KEY | PROJECT_ID | PHASE
1 100 Phase-1
2 200 Phase-2
3 300 Phase-3
4 400 Phase-4
5 500 Phase-5
select * from b;
PRIMARY_KEY | PROJECT_NUMBER
100 null
200 2000
300 3000
400 null
500 5000
select * from c;
PRIMARY_KEY | NUMBER_COL | LENGTH_COL | DATE_COL
100 null 99 null
200 null 99 null
300 null 99 null
400 null 99 null
500 null 99 null
select * from d;
PROJECT_ID | COLOR
100 black
200 red
300 blue
400 black
500 yellow
select * from TableContacts;
PROJECT_NUMBER | LOOKUP_COLUMN
1000 l-1000
2000 l-2000
3000 l-3000
4000 l-4000
5000 l-5000
Existing query in question returns this:
SELECT a.primary_key,
a.phase,
b.project_number,
c.LENGTH_col,
d.color
FROM a,b,c,d
WHERE c.primary_key = a.PROJECT_ID
AND b.primary_key = a.PROJECT_ID
AND b.primary_key = d.project_ID
AND (c.date_col IS NULL OR c.number_col IS NULL)
AND d.color IN ('black','red','blue')
ORDER BY 1;
PRIMARY_KEY | PHASE | PROJECT_NUMBER | LENGTH_COL | COLOR
1 Phase-1 null 99 black
2 Phase-2 2000 99 red
3 Phase-3 3000 99 blue
4 Phase-4 null 99 black
The goal is to populate the lookup_column where project_number is not null. Running the union query provided at start of answer:
select t1.primary_key, t1.phase, t1.project_number, t1.length_col, t1.color, TableContacts.lookup_column
from t1, TableContacts
where t1.project_number = TableContacts.project_number
UNION
select t1.primary_key, t1.phase, t1.project_number, t1.length_col, t1.color, null
from t1 where t1.project_number is null;
PRIMARY_KEY | PHASE | PROJECT_NUMBER | LENGTH_COL | COLOR | LOOKUP_COLUMN
1 Phase-1 null 99 black null
2 Phase-2 2000 99 red l-2000
3 Phase-3 3000 99 blue l-3000
4 Phase-4 null 99 black null