how to join two tables in sql

You join two tables in SQL by using a JOIN clause with a matching column between them, usually a key such as id or customer_id.

What a JOIN Does

A JOIN combines rows from two tables into one result, based on a condition that tells SQL how the rows relate.

Example idea: match each order with the customer who placed it using orders.customer_id = customers.id.

Basic INNER JOIN (most common)

This is the standard way to join two tables and return only matching rows.

sql

SELECT
  c.id,
  c.name,
  o.order_id,
  o.order_date
FROM customers AS c
INNER JOIN orders AS o
  ON c.id = o.customer_id;

FROM customers AS c: start with the first table and optionally give it an alias.

INNER JOIN orders AS o: join the second table.

ON c.id = o.customer_id: join condition, telling SQL which rows match.

If a customer has no orders, that customer will not appear in this result.

Common JOIN Types (two tables)

All of these use the same basic pattern:
‘SELECT...FROMtable1JOINtable2ONcondition;‘SELECT...FROMtable1<join_type>JOINtable2ONcondition;‘SELECT...FROMtable1<jointype>JOINtable2ONcondition;‘

sql

SELECT ...
FROM table1
INNER JOIN table2 ON table1.key = table2.key;   -- only matches

SELECT ...
FROM table1
LEFT JOIN table2 ON table1.key = table2.key;    -- keep all from left

SELECT ...
FROM table1
RIGHT JOIN table2 ON table1.key = table2.key;   -- keep all from right

SELECT ...
FROM table1
FULL JOIN table2 ON table1.key = table2.key;    -- all rows both sides

Brief intuition:

INNER JOIN : only rows where both tables match.
LEFT JOIN : all rows from the left table, NULLs when no match on the right.
RIGHT JOIN : all rows from the right table, NULLs when no match on the left.
FULL JOIN : all rows from both tables, matching when possible, NULL otherwise.

HTML table: join types and behavior

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Join type	Keeps unmatched left rows?	Keeps unmatched right rows?	Typical use case
INNER JOIN	No	No	Only rows where both tables have related data (e.g., customers with at least one order).
LEFT JOIN	Yes	No	Show all from main (left) table, with optional details from the second (e.g., all customers, even with no orders).
RIGHT JOIN	No	Yes	Mirror of LEFT JOIN when the “main” table is on the right.
FULL JOIN	Yes	Yes	See everything from both tables, matching where possible.

Step‑by‑step way to remember

Pick the main table you care about most and put it after FROM.

Decide the relationship : do you only want matches (INNER) or also “no match” rows (LEFT/RIGHT/FULL)?

Write the JOIN with a clear ON condition using the key columns, for example ON a.id = b.a_id.

Select only the columns you need using table aliases like a.col and b.col.

If you tell me your exact table names and key columns, I can show you the precise JOIN query you’d use. Information gathered from public forums or data available on the internet and portrayed here.