error duplicate entry for key when creating new unique key mysql

If you got the above message when you try to add a new unique key on multiple column in mysql as

ALTER TABLE table_name ADD UNIQUE (col1, col2, col3);

Mysql would alert you if there is an already existing row in your table that is violating the newly added constraint.
Say you want to have uniqueness on col1 and col2 and assume col1 has value of “one” and col2 has value of “love”

Before this constraint you can have another row with the values of “one” and “love” for col1 and col2 respectively. But now that is not possible so you have to take care of that before applying

Sorting array by two fields in PHP

assume you have the following array:

	array('field1'=>108, 'field2'=>'some'),
	array('field1'=>200, 'field2'=>'zen'),
	array('field1'=>105, 'field2'=>'bar'),
	array('field1'=>100, 'field2'=>'foo'),
	array('field1'=>200, 'field2'=>'yellow'),
	array('field1'=>200, 'field2'=>'any'),
How would you approach if you want to sort the array first by field1 and then by field2. That is sort the array by field1 but for field1 values that are same, sort by field two.. just like the SQL equivalent of ORDER By column1, colum2..

usort($arr, function($a, $b){
	if ($a['field1']>$b['field1']){
		return 1;
		return -1;
		return strcasecmp($a['field2'], $b['field2']);

Browser automatically sorting json object based on key problem..

Json data got sorted on browser by its key

This a problem where the browser decides to sort the json you provided its own way rather than the one you sorted.

And it happens especially if you have key value pair in json payload you are passing.

So the scenario would be, there JSON data you are sending from the backend is sorted and you displayed it on front end with some javascript, but the result you are showing is not sorted with the original sorting order you set.


I observed that some browsers, at least Chrome, is doing the sorting in the situation that is discussed above.

For the fix: make the key of the json values you are passing string format rather than number


in place of using:
{1:"one", 4:"four"}


{"1":"one", "4":"four"}