mysql join query where multiple rows have same key value - mysql

Question

I have a table, in a third party database, that has two tables like these:
HISTORY
========
ID | ORDERED
1 PEAS
1 CARROTS
1 SPINACH
2 CARROTS
3 PEAS
3 CARROTS
PEOPLE
=====
ID | NAME
1 Jamal
2 Sharon
3 Mark
I am trying to create a MYSQL query that will return all the PEOPLE who ORDERED both PEAS and CARROTS. The results would be:
Jamal, Mark
When I try this with the OR operator, I get all three people:
SELECT a.ID from people a
INNER JOIN history b on a.ID=b.ID
WHERE b.ordered='PEAS' OR b.ordered='CARROTS'
When I try this with the AND operator, I get no people.
SELECT a.ID from people a
INNER JOIN history b on a.ID=b.ID
WHERE b.ordered='PEAS' AND b.ordered='CARROTS'
How can I write a query to get the names of the people who ordered peas and carrots given the table structure I have to work with?

Answer 1

JOIN twice, once for each condition:
SELECT a.ID
FROM people a
JOIN history b on a.ID=b.ID AND b.ordered='PEAS'
JOIN history c on a.ID=c.ID AND c.ordered='CARROTS'
If history can contain duplicates, or to be defensive, add DISTINCT:
SELECT DISTINCT a.ID
FROM ...

Answer 2

Select all people from people and for each of them the history details, but only the people who ordered PEAS or CARROTS:
When you say "all" people, then you always begin your sql with the people table. When you say "who have", then you add the LEFT JOIN, e.g to the LEFT table (people) you JOIN the wanted details from the right table (history). And when you say "but just the ones having the following details", then you apply a filter, e.g. you use WHERE clause.
SELECT
peo.ID, -- OPTIONAL
peo.NAME,
his.ID, -- OPTIONAL
his.ORDERED
FROM people AS peo
LEFT JOIN history AS his ON his.ID = peo.ID
WHERE
his.ORDERED = "PEAS" OR
his.ORDERED = "CARROTS"
;
Note: "--" means commentar.
EDIT 1:
Important, a principle which you always should apply: Rename the history.ID column to history.PEOPLE_ID and add a new column history.ID as PRIMARY KEY column, in order to uniquely identify each historyrecord.
HISTORY
-------
ID PEOPLE_ID ORDERED
1 1 PEAS
2 1 CARROTS
3 1 SPINACH
4 2 CARROTS
5 3 PEAS
6 3 CARROTS
PEOPLE table remains the same.
EDIT 2:
NO no, it should be an AND in the WHERE clause. My fault. I corrected it.
EDIT 3:
NO no, it should be an OR in the WHERE clause. My fault. I corrected it. AGAIN :-)))