在包含外部引用的被聚合表达式中指定了多个列。如果被聚合的表达式包含外部引用，那么该外部引用就必须是该表达式中所引用的唯一的一列。

Multiple columns are specified in an aggregated expression containing an outer reference. If an expression being aggregated contains an outer reference, then that outer reference must be the only column referenced in the expression.