How do I say WHERE (a = 1 OR b =1 ) AND (c = 1 OR d = 1)
For more complicated queries am I supposed to use raw SQL?
Make use of Logical Grouping (Laravel 7.x/4.2). For your example, it'd be something like this:
Model::where(function ($query) {
    $query->where('a', '=', 1)
          ->orWhere('b', '=', 1);
})->where(function ($query) {
    $query->where('c', '=', 1)
          ->orWhere('d', '=', 1);
});
function ($query) use ($param1, $param2)...; Oh, you deleted your comment.If you want to use parameters for a,b,c,d in Laravel 4
Model::where(function ($query) use ($a,$b) {
    $query->where('a', '=', $a)
          ->orWhere('b', '=', $b);
})
->where(function ($query) use ($c,$d) {
    $query->where('c', '=', $c)
          ->orWhere('d', '=', $d);
});
Incase you're looping the OR conditions, you don't need the the second $query->where from the other posts (actually I don't think you need in general, you can just use orWhere in the nested where if easier)
$attributes = ['first'=>'a','second'=>'b'];
$query->where(function ($query) use ($attributes) 
{
    foreach ($attributes as $key=>value)
    {
        //you can use orWhere the first time, doesn't need to be ->where
        $query->orWhere($key,$value);
    }
});
use keyword to use the attributes variable inside the where.if you want to use parentheses in laravel 4 and don't forget return
In Laravel 4 (at least) you need to use $a, $b in parentheses as in the example
$a = 1;
$b = 1;
$c = 1;
$d = 1;
Model::where(function ($query) use ($a, $b) {
    return $query->where('a', '=', $a)
          ->orWhere('b', '=', $b);
})->where(function ($query) use ($c, $d) {
    return $query->where('c', '=', $c)
          ->orWhere('d', '=', $d);
});
Simply Use in Laravel Eloquent:
$a='foo', $b='bar', $c='john', $d='doe';
Coder::where(function ($query) use ($a, $b) {
    $query->where('a', '=', $a)
          ->orWhere('b', '=', $b);
})->where(function ($query) use ($c, $d) {
    $query->where('c', '=', $c)
          ->orWhere('d', '=', $d);
})->get();
Will produce a query like:
SELECT * FROM <table> WHERE (a='foo' or b='bar') AND (c='john' or d='doe');
Another way without using Modal
Database: stocks 
Columns:id,name,company_name,exchange_name,status

  $name ='aa'
  $stocks = DB::table('stocks')
            ->select('name', 'company_name', 'exchange_name')
            ->where(function($query) use ($name) {
                $query->where('name', 'like', '%' . $name . '%')
                ->orWhere('company_name', 'like', '%' . $name . '%');
            })
            ->Where('status', '=', 1)
            ->limit(20)
            ->get();
ModelName::where(function ($query) use ($a) {
    $query->where('a', '=', $a)->orWhereNull('a');
})
->where(function ($query) use ($b,$c) {
    $query->where('b', '=', $b)
          ->orWhere('c', '=', $c);
})
->where('d',$d);
OUTPUT QUERY:
SELECT * FROM ModelName WHERE (a='a' or a is null) AND (b='b' or c='c') AND d='d';
You can also use query scopes to make things a bit tidier, so you can do something like:
Invoice::where('account', 27)->notPaidAt($date)->get();
Then in your model
public function scopeNotPaidAt($query, $asAt)
{
    $query = $query->where(function ($query) use ($asAt) { 
        $query->where('paid', '=', '0000-00-00')->orWhere('paid', '>=', $asAt); 
    });
    return $query;    
}
Best way to use sql brackets use callback function in laravel eloquent.
YourModal::where(function ($q) {
    $q->where('a', 1)->orWhere('b', 1);
})->where(function ($q) {
    $q->where('c', 1)->orWhere('d', 1);
});
You don't have to use
=symbol, it's come as the default
Lest say if you have a query that contain brackets inside a brackets
WHERE (a = 1 OR (b = 1 and c = 5))
YourModal::where(function ($q) {
    $q->where('a', 1)->orWhere(function($q2){
      $q2->where('b', 1)->where('c', 5);
    });
});
lest say you want to make values dynamics
YourModal::where(function ($q) use($val1, $val2) {
    $q->where('a', $val1)->orWhere(function($q2) use($val2){
      $q2->where('b', $val2)->where('c', $val2);
    });
});
For eloquent query builder the following query will not work:
MODELNAME::where('a', 1)->orWhere('b', 1)->where('c', 1)->orWhere('d', 1);
But you can use this code:
MODELNAME::where(function($a) {
    $a->where('a', 1)->orWhere('b', 1);
})->where(function($a) {
    $a->where('c', 1)->orWhere('d', 1);
});
You can use the second query and it will work perfectly.
If you are using PHP 7.4+ you can also use arrow functions. They automatically capture variables from the surrounding scope, so you don't need to use the use() keyword.
Model::query()
  ->where(fn($query) => $query->where("a", "=", $a)->orWhere("b", "=", $b))
  ->where(fn($query) => $query->where("c", "=", $c)->orWhere("d", "=", $d));