PHP variable value to NOT update MySQL table field? - php

Question

I'm updating a MySQL table with posted PHP data.
I first gather the posted data, and put them in appropriate variables. Together with the necessary if/else checks.
Then, I only have to write my query once.
But now I have an if/else to check wether to update a specific field or not. How can I store a "do-not-update" value inside the corresponding variable?
Because otherwise I have to put an if/else check around the whole query, just for one field.
I just want to be as efficient as possible. :)
My query is as follows:
$updateTable = mysql_query("UPDATE myTable SET field1 = '$field1', field2 = '$field2'");

Answer 1

wherever you are get $_POST into variables, do this,
if( $field2 === 'xyz' ) { //if value is 'xyz', do not update
$sql = '';
} else
$sql = ", field2 = '$field2'";
Then in the query,
$updateTable = mysql_query("UPDATE myTable SET field1 = '$field1' $sql");
Edit: if using 1/0 (true or false),
if( $field2 == true ) { //if value is true, do not update
$sql = '';
} else
$sql = ", field2 = '$field2'";

Answer 2

You will need to build up your query, storing it in a PHP string, for example:
$sql = "UPDATE `table` SET ";
if ($_POST['foo']!=='') {
$sql .= " `foo`='".mysql_real_escape_string($_POST['foo'])."',";
}
if ($_POST['bar']!=='') {
$sql .= " `bar`='".mysql_real_escape_string($_POST['bar'])."',";
}
$sql = rtrim($sql,',');
$sql .= " WHERE `id`='".mysql_real_escape_string($_POST['id'])."'"
Then execute your string as the query.

Answer 3

If you are asking whether the field should be updated, you can do one of two things:
1) Specify a criteria that ensures field1 and field2 are only updated if the rows match the criteria. If the criteria does not match, the record will not be updated. This is the most common way.
UPDATE myTable ...
WHERE criteria1 = 1 AND criteria2 = 'Red'
2) Run a query before the UPDATE to see whether to perform an update.

Answer 4

I'm not exactly sure what you are asking for, but perhaps this answers your question:
$updateTable = mysql_query("
UPDATE myTable SET
field1 = IF('$field1'>'','$field1', field1),
field2 = IF('$field2'>'','$field2', field2)
");
Of course, you are opening yourself up to SQL injection with the code, as written.

Answer 5

Lets assume you have gathered the fields to update in an array $fields like this :
array (
'filed1' => 'value' ,
'field2' => ''value
)
Now you need to generate the query, you can do this by looping in the array:
$sql = "UPDATE mytable ";
$sql .= $fields ? "SET " : "" ;
foreach ($fields as $key=>$value) {
$sql.= $value ? "$key = '$value' , " : '' ;
}
//you need to omit the trailing ','
$sql[strlen($sql) -1 ] = "";
Tips :
Do sanitize all user input using mysqli_real_escape_string or something better than that.
Happy coding :)