Viewing Data from two tables while linking multiple tables in SQL - sql

Question

I am trying to set up a view in a database I want to see all the data in the PERSON table and three columns from the NON_PERSONNEL table for a program from the PROGRAM table. This is what I am trying now, the query runs without errors but doesnt give me any results. All 4 of the tables listed below are imperative to derive the answer
SELECT
person.*,
non_personnel.description,
non_personnel.amount
FROM
person,
non_personnel,
personnel_role,
programs
WHERE
person.person_id = personnel_role.person_id
AND personnel_role.program_id = programs.program_id
AND programs.program_id = non_personnel.program_id
AND programs.program_name = 'Fake Program'

Answer 1

you need to use left join, so you get all persons but description and amount can be NULL if that person doesn't have records in other tables
Also use explicit join syntax.
SELECT person.*, non_personnel.description, non_personnel.amount
FROM person
left join personnel_role
ON person.person_id = personnel_role.person_id
left join programs
ON personnel_role.program_id = programs.program_id
AND programs.program_name = 'Fake Program'
left join non_personnel
ON programs.program_id = non_personnel.program_id

Answer 2

This really depends on your schema and the data in the tables. The way you have it written now means that only records that match in every table (according to your WHERE conditions) are passed into the result set.
This means that you have to have all program_id's in your programs table that you want returned in the results ALSO in your non_personnel table. They must also ALL be in your personnel_role table. And all person_ids in your personnel_role table must be in the person table. You get no results back, so this is probably not what you meant to write.
My guess is that you want to use a LEFT OUTER JOIN here. LEFT OUTER JOIN says "Take all records from one table and ONLY records from the joined table that meet the criteria in your ON statement".
Because you are wanting information based on a particular Program, chances are you want to start with that table:
SELECT person.*,
non_personnel.description,
non_personnel.amount
FROM
programs
LEFT OUTER JOIN personnel_role ON
programs.program_id = personnel_role.program_id
LEFT OUTER JOIN person ON
personnel_role.person_id = person.person_id
LEFT OUTER JOIN non_personnel
programs.program_id = non_personnel.program_id
WHERE
programs.program_name = 'Fake Program'
This is a bit of an assumption since I have no idea what your schema is or how your data is built, but I'm betting it's what you are after.
What this FROM clause says is:
1. Take all records from Program (where program_name = 'fake program') and only reocrds from personnel_role that share the same program_id
2. Take only the records from person where the person_id matches the records we just got from the personnel_role table
3. Take only the records from non_personnel where it shares a program_id with the results from the program table.