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                在處理大規模數據集時,在開發和修改查詢的階段,如果能在數據集的一小部分數據上試運行查詢,會帶來很多方便。 <br/> ```sql # 分桶抽樣基本語法 select * from table_name tablesample(bucket x out of y on param) s; -- x:要從第x個分桶開始查詢,x <= y; -- y:抽樣比例,比如分桶總數為4,y=2,則抽取y=4/2=2個分桶; 如果分桶總數為4,y=8,則抽取y=4/8=1/2個分桶; 注意:y必須是分桶總數的倍數或因子。 -- param:可以是分桶表的一列或多列,或者是一個有返回值的函數,比如隨機函數rand() -- s:表的別名 #### #### select * from bucket_4 tablesample(bucket 2 out of 8) s; #### 根據id列查詢 ##### select * from bucket_4 tablesample(bucket 2 out of 48 on id) s; #### 根據整行隨機抽樣 #### select * from bucket_4 tablesample(bucket 2 out of 48 on rand()) s; ```
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