PHP, SWITCH statement, and NULL Values

[snorky]

PHP 4.3.8

 

I can't figure out the correct syntax for the case condition in a switch statement where one of the case conditions is a NULL value.  :facewall:

 

For a switch statement I have 3 conditions:

 

[*]variable's value is NULL // NULL

[*]variable's value is "" // blank & NOT NULL

[*]variable's value is "abcdef" // not blank (and therefore NOT NULL)

 

The switch statement looks like this

switch(var)
{
case * (where * is some kind of NULL -- see below):
	do something #0;
	break;

case ""
	do something #1;
	break;

case "!=''"
	do something #2;
	break;
}

* Case NULL is the joker in the deck. I've tried it 5 different ways.

 

case "= NULL":

case NULL:

case "NULL":

case IS_NULL():

case "IS_NULL()":

 

None of the 5 works correctly when the condition is a NULL value. Each of those has a different -- and incorrect -- result set for

variable's value is NULL // NULL

variable's value is "" // blank & NOT NULL

variable's value is "abcdef" // not blank (and therefore NOT NULL)

[wildteen88]

You're using case wrong, but case null: should work.

 

switch only compares the value of the variable you pass it. It does not allow you perform any conditions.

 

$var = null;

switch($var)
{
    case null:
       echo '$var is NULL';
    break;

    case '':
       echo '$var has no value or is emtpy';
    break;
}

[snorky]

You're using case wrong, but case null: should work.

 

switch only compares the value of the variable you pass it. It does not allow you perform any conditions.

 

$var = null;

switch($var)
{
    case null:
       echo '$var is NULL';
    break;

    case '':
       echo '$var has no value or is emtpy';
    break;
}

 

/* ---------------------- */

 

The goal is to produce a report. There is a while loop that spins out the report based on what happens in the while loop. The report looks fine (except that one column): all of the other elements of the report - including some generated by other switch statements (none of which have NULL as a possible value) - look as designed.

 

(Note: I changed :one" to NONE" - oops!)

 

Here's how I got the variable where NULL is a possible value:

The table has a column named emdiff.

The PHP to produce the report is next:

 

while($row=mysql_fetch_array($rpt1))

    ....

    $emdiff= $row["emdiff"];

// note: there several other columns in this mysql_fetch_array

// all of them work as designed - including switch statements - but none of them has a condition where NULL is one of the possible values

// in the process, values are assigned to $var2 and $var3

    ....

 

Then the switch statement in question:

switch($emdiff)
{
   case * (where * is some kind of NULL -- see below):
      print "";
      break;

   case ""
      print $emdiff . " abcdef";
      break;

   case "!=''"
      print $var2 . $var3;
      break;

}  // end switch statement

} // end while loop

In the result set

a. when $emdiff is  NULL the field displays as designed (meaning: it displays an empty result)

b. when $emdiff is  =""    print $emdiff . " abcdef"; does not display, even though it should display

c. when $emdiff is  !=""  print $var2 . $var3;  displays as designed

 

When I use the other attempts at case * (some expression of NULL),  I get various mixes of a, b, and c

 

[snorky]

In the above,

The report looks fine (except that one column): all of the other elements of the report - including some generated by other switch statements (one of which has NULL as a possible value) - look as designed

 

Should read

 

The report looks fine (except that one column): all of the other elements of the report - including some generated by other switch statements (NONE of which have NULL as a possible value) - look as designed.

 

That oopsie changes a lot.... sorry for the confusion.

[snorky]

I came up up with a way to get the desired result. It's kludgey, involving nested if-else statements.

 

<?php
// there are 3 possible values for $emdiff:
// NULL, "" (blank), and (non-blank)
if(isset($emdiff))		// if emdiff is NOT NULL
{
if($emdiff !='')	// emdiff is NOT NULL and NOT blank 
{
	do task a;
}
else			// emdiff is NOT NULL and is blank(empty)
{		
	do task b;
}     
}
else				//	otherwise, emdiff is NULL
{
do task c;
}
?>

 

If anyone can come up with a more elegant solution, I'd love to see it. I suspect that a switch/case would be better, but I struck out dozens of times trying.