How to select multiple tables using mysql?

Question

Okay, so far I can select two tables using mysql but I cant select three or more tables using mysql how can I select more then three tables using mysql.

Here is the code below.

SELECT users.*, oldusers.* FROM users, oldusers WHERE users.user_id='$user_id' = oldusers.user_id

I'm trying to add all the tables contents into something like this.

while($row = mysqli_fetch_array($dbc)){ 
    $first_name = $row["first_name"];
    $last_name = $row["last_name"];

}

Answer 1

I think you're looking to use an INNER JOIN - where you group together tables based on the same column. What's your exact purpose?

SELECT users.*, oldusers.*, anotherTable.*

FROM users

INNER JOIN oldusers ON oldusers.user_id = users.user_id
INNER JOIN anotherTable ON oldusers.user_id = anotherTable.anotherid

WHERE users.user_id = 'something'
// AND anotherTable.foo = 'bar'

Answer 2

Here's one way:

SELECT table1.column1, table2.column2 
  FROM table1, table2, table3 
  WHERE table1.column1 = table2.column1 
  AND table1.column1 = table3.column1;

Pretty much a join...

Here's another way:

SELECT column1, column2, column3 
  FROM table1 
  UNION 
SELECT column1, column2, column3 
  FROM table2 
  UNION 
SELECT column1, column2, column3 
  FROM table3;