据我所知(如果我错了，请纠正我)，SQL中没有文字布尔值的概念.您可以让表达式评估为布尔值，但不能输出它们.

To my knowledge (correct me if I'm wrong), there is no concept of literal boolean values in SQL. You can have expressions evaluating to boolean values, but you cannot output them.

这就是说，您可以使用CASE WHEN生成可以在比较中使用的值:

This said, you can use CASE WHEN to produce a value you can use in a comparison:

SELECT 
    CASE WHEN ValueColumn IS NULL THEN 'FALSE' ELSE 'TRUE' END BooleanOutput 
FROM 
    table