Q&A

Q1:I have run a join but get many thousands of rows of data in my resultset, when each table only has a few hundred rows. Help!
A1: You probably didn't use the JOIN keyword, but listed several tables in your FROM clause. You may have done something like this: 
SELECT * FROM table1, table2

Right? This is a common mistake. You performed a cross join when you meant to do a different type of join. You forgot to specify the relationship between the two tables.

The solution is to change your SQL to look like this:

SELECT * FROM table1, table2
  WHERE table1.id_col = table2.id_col

or to write your SQL using the JOIN keyword, like this:

SELECT *
  FROM table1
  INNER JOIN table2
  ON table1.id_col = table2.id_col
Q2:Can I join more than two tables?

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