I'm struggling with some PHP/MySQL code. I am reading from 1 table, changing some fields then writing to another table, nothing happens if inserting and one of the array values is null when I would like it to insert null in the database (null values are allowed for the field). It looks a bit like this:
$results = mysql_query("select * from mytable");
while ($row = mysql_fetch_assoc($results) {
mysql_query("insert into table2 (f1, f2) values ('{$row['string_field']}', {$row['null_field']});
}
Not every row has a null value and in my query there are more fields and 2 columns which may or may not be null
This is one example where using prepared statements really saves you some trouble.
In MySQL, in order to insert a null value, you must specify it at INSERT time or leave the field out which requires additional branching:
INSERT INTO table2 (f1, f2)
VALUES ('String Value', NULL);
However, if you want to insert a value in that field, you must now branch your code to add the single quotes:
INSERT INTO table2 (f1, f2)
VALUES ('String Value', 'String Value');
Prepared statements automatically do that for you. They know the difference between string(0) "" and null and write your query appropriately:
$stmt = $mysqli->prepare("INSERT INTO table2 (f1, f2) VALUES (?, ?)");
$stmt->bind_param('ss', $field1, $field2);
$field1 = "String Value";
$field2 = null;
$stmt->execute();
It escapes your fields for you, makes sure that you don't forget to bind a parameter. There is no reason to stay with the mysql extension. Use mysqli and it's prepared statements instead. You'll save yourself a world of pain.
For fields where NULL is acceptable, you could use var_export($var, true) to output the string, integer, or NULL literal. Note that you would not surround the output with quotes because they will be automatically added or omitted.
For example:
mysql_query("insert into table2 (f1, f2) values ('{$row['string_field']}', ".var_export($row['null_field'], true).")");
I think you need quotes around your {$row['null_field']}, so '{$row['null_field']}'
If you don't have the quotes, you'll occasionally end up with an insert statement that looks like this: insert into table2 (f1, f2) values ('val1',) which is a syntax error.
If that is a numeric field, you will have to do some testing above it, and if there is no value in null_field, explicitly set it to null..
Source: Stackoverflow.com