yii2在查询中选择NULL值（选择NULL作为列，...）

Question

Is there a way to select NULL value or an exact string in a query in YII2? I am trying to join 3 queries and I need the same number of columns queries and something like "select NULL as returned, submitted, amount, NULL as iamount....." Example:

$subQuery2 = Loan::find()->select('person_id')->where(['sheet_id' => $id]);

$query2 = new Query();$query2 = new Query();
$query2->select(['last_name','first_name','fc.tax','NULL as returned','fc.submitted','fc.amount','NULL as iamount','NULL as interest',
        'b.month','b.year','b.nb']) 

    ->from('sheet as b')
    ->join('JOIN', 'fee as fc',
            'b.id  = fc.sheet_id')     
    ->join('JOIN','person','fc.person_id = person.id')
    ->where(['b.id' => $id])
    ->andWhere(['not in', 'person_id', $subQuery2]);  

$query = new Query();

$query->
select(['last_name','first_name','fc.tax','fi.returned','fc.submitted','fc.amount','fi.amount as iamount','fi.interest',
        'b.month','b.year','b.nb']) 

    ->from('sheet as b')
    ->join('RIGHT JOIN', 'fee as fc',
            'b.id  = fc.sheet_id')     
    ->join('JOIN','person','fc.person_id = person.id')
    ->join('LEFT JOIN','loan as fi',
        'b.id = fi.sheet_id and fc.person_id = fi.person_id')
    ->where(['b.id' => $id])
    ->union($query2)
    ->orderBy(['last_name' => SORT_DESC]);

Answer 1

Yes, you have two ways to do it:

    $query = new Query();
    $query->select([
         new Expression('NULL as test')
         'test2' => new Expression('NULL'), 
    ])->from('sheet as b');

Both of selects will do the same, but the second line ( test2 ) is preferable as it is more DBMS-agnostic.