Displaying variables in text - clarification needed

Hello all. I inherited some PHP pages about a year ago. They have been fine all along but now a bunch of erroneous errors and results are popping up. I traced it to the way the variables were being used on the page... for example, the following SQL statement (a space between ' and " for clarity): sql="select name from mytable where name=$myvar and display='yes' "; This has worked in the past but is now returning errors for some records and working for others. I changed the above to the following and now all is good: sql="select name from mytable where name=' ".$myvar." ' and display='yes' "; What would explain why the former is suddenly causing problems? The version of PHP is 5.2.3 and from what I can tell, hasn't been updated since February of 2011. Thanks, --Rick