Tuesday 27 November 2012

MySQL LEFT JOIN

The LEFT JOIN keyword returns all rows from left table and returns match rows from right table.

family Table:

PositionAge
Dad41
Mom35
Daughter17
Dog12

food Table:

MealPosition
RiceDad
DosaMom
Idly
EggDog

When we decide to use a LEFT JOIN in the query instead, all the family members be listed, even if they do not have a favorite dish in our food table.
This is because a left join will preserve the records of the "left" table.
 
<?php 
/* Make a MySQL Connection */
$query = "SELECT family.Position, food.Meal FROM family LEFT JOIN food ON 
family.Position = food.Position";
  
$result = mysql_query($query) or die(mysql_error());


// Print out the contents of each row into a table 
while($row = mysql_fetch_array($result)){
 echo $row['Position']. " - ". $row['Meal'];
 echo "
";
}
?>
Output:-
Dad - Dosa Mom - Rice Daughter - NULL Dog - Egg

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