PHP，合并两个数组，删除相同的值

Question

Is there a better way how to do it? Some one function in PHP?

  $a = array(1, 2, 3, 4, 5, 6);
  $b = array(1, 2, 8, 9, 10, 3, 20);

  $c = array_merge($a, $b);
  $c = array_unique($c);

Result: 1, 2, 3, 4, 5, 6, 8, 9, 10, 20

Or is there some way how to do it in MySQL? In case that:

$a = getMySQLArray("SELECT id FROM table1 WHERE ...")
$b = getMySQLArray("SELECT id FROM table2 WHERE ...")

I need to do two steps(two SELECT) to get all ids which I need but sometimes both array can contain the same id so I need to filter it. I'm not so expert with SQL to create some more complex SQL request. It is possible to create something like this?

Answer 1

You can use a single query to get those distinct values with UNION :

SELECT 
    id 
FROM table1 WHERE ...
UNION
SELECT 
    id 
FROM table2 WHERE ...

UNION without the keyword ALL will only return distinct rows, in your case distinct values.

SELECT ...
UNION [ALL | DISTINCT] SELECT ...
[UNION [ALL | DISTINCT] SELECT ...]

UNION is used to combine the result from multiple SELECT statements into a single result set. ...

The default behavior for UNION is that duplicate rows are removed from the result.