yii2 如何选取表中不存在字段 生成类似语句 select "a" as b from table

Question

如题
翻了下手册没找到
另外 如何只在select内执行原生语句？
例如 $query = self::find()->select(自定义语句) 有这种写法吗？

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自己找到了....

$select = new Expression("'a' as b");
$query = self::find()->select($select)

Answer 1

$select = new Expression("'a' as b");
$query = self::find()->select($select)