Sum 41 Cancels Australian Tour Following Deryck Whibley Pneumonia Diagnosis ’s Cancelled After Illness Axs Tv

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关键区别在于：在使用 `sum (case when )` 时，`case when` 语句中的判断字段必须是 `group by` 中的分组字段。而 `case when sum ()` 方法则相对灵活，但需要注意的.

Sum 41 Cancels Australian Tour Following Deryck Whibley's Pneumonia