Unknown column '' in 'where clause'

Question

My query is throwing up this error. Can anyone see why?

$query = "SELECT * FROM Units WHERE ID = `$uniqueUnits[a]`";

Unknown column '' in 'where clause'

Answer 1

Two problems.

• You're using backticks to delimit a string. Backticks delimit fields, so MySQL thinks you're trying to give it a column name.

• The error message indicates that, in fact, this value that it thinks is a column name, is empty. So your value $uniqueUnits[a] is probably broken, or not being interpolated correctly.

---

You should do the following:

• Interpolate your variables explictly with the "complex syntax" to be sure that the string forms properly;

• Check the value of $query so that you can see what's going on:

  print $query;
  

• Use actual quotation marks to delimit strings:

  $query = "SELECT * FROM Units WHERE ID = '{$uniqueUnits[a]}'";
  //                                       ^ quote
  //                                        ^ PHP variable interpolation
  

Answer 2

try

$query = "SELECT * FROM Units WHERE ID = '$uniqueUnits[a]'";
                                         ^---            ^---

Backticks are for escaping reserved words, so mysql is translating your variable's contents into a field name.

Answer 3

Because apparently $uniqueUnits[a] resolves to the empty string. And there is no column like this in the database.

Answer 4

Try surrounding your array with {}, like this:

$query = "SELECT * FROM Units WHERE ID = `{$uniqueUnits[a]}`";

Also, is column ID actually in your table?