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å设åaçå¼ä¸º20ï¼åbçå¼ä¸º12ï¼å®ä»¬é½æ¯æ°å¼åï¼
å·®select a-b from table;
ç»æ为:
a-b
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(select * from a) minus (select * from b);
ç»æ为ï¼
两表差å¼æ°æ®;
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