How Can I Combine User Data from Multiple Tables Using SQL Joins?

Understanding SQL Joins: Querying Multiple Tables

Problem:

You have two tables, "A" and "B," containing user data and addresses. You want to retrieve a result that combines these data, aligning users with their corresponding addresses.

Query Development:

The most suitable SQL join for this problem is a left outer join, which retrieves all records from the left table ("A") and includes matching records from the right table ("B") if available.

SQL Query:

SELECT A.uid, A.name, B.address
FROM A
LEFT JOIN B ON A.uid = B.uid;

This query will return the desired result, displaying user IDs, names, and addresses as follows:

uid	name	address
1	test1	address1
2	test2	address2
3	test3	NULL
4	test4	address3

Explanation:

• The FROM A clause indicates that we start with table "A."
• The LEFT JOIN B ON A.uid = B.uid clause performs a left outer join on the condition that the uid column in table "A" matches the uid column in table "B."
• This join ensures that all users in table "A" are included in the result, regardless of whether they have an address in table "B."
• If a matching address is found in table "B," it is displayed in the address column; otherwise, the column displays NULL.

Visual Representation of SQL Joins:

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