JOINs

ধরুন:

users

user_id   name
1         Rahim
2         Karim
3         Shuvo

orders

order_id  user_id
101       1
102       1
103       2

INNER JOIN

Only matching users।

SELECT *
FROM users u
INNER JOIN orders o
    ON u.user_id = o.user_id;

Shuvo থাকবে না।

Left table-এর সব users।

SELECT *
FROM users u
LEFT JOIN orders o
    ON u.user_id = o.user_id;

Shuvo থাকবে।

Order columns:

NULL

Users যাদের কোনো order নেই:

SELECT
    u.user_id,
    u.name
FROM users u
LEFT JOIN orders o
    ON u.user_id = o.user_id
WHERE o.order_id IS NULL;