title: SQL JOIN two tables and duplicate rows appear
body: <p>Looking for ideas as to why my <strong>JOIN</strong> statement duplicates rows. 
  I have two tables and join them with <strong>JOIN</strong>, <strong>LEFT</strong> or <strong>RIGHT</strong> conditions. Now something interesting happens, even with no added data from the second table my rows from first table duplicate. So, in table 1 I have 3 rows and after any <strong>JOIN</strong> it goes to 9 (3 x 3 duplicates) and I only have data from table 1 in my <strong>SELECT</strong>. </p>
  
  <p>I tried multiple selects including <strong>GROUP BY</strong> with no luck so far. Can you please direct me towards the root cause?</p>