MySql的分組數據(創建分組，分組中帶總計，過濾分組數據，分組數據排序，select語句執行順序)

1.創建分組(group by) 示例：查詢一共有多少條數據，按照vend_id的不同來分組顯示 select vend_id,count( * ) from products group by vend_id; 2.創建摘要(with rollup) 示例:同上，上面不帶總計，需要加上對應關鍵字 select vend_id,count( * ) from products group by v

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