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oracle中and和or
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复习ocp考题的时候有道关于and和or的题目,拿出来看一下and和or的区别:
Choose two
Examine the description of the BOOKS_TRANSACTIONS table
Name Null? Type
----------------------------------------------------------------------------------------------
THANSACTION_ID NOT NULL VARCHAR2(6)
TRANSACTION_TYPE VARCHAR2(3)
BORROWED_DATE DATE
BOOK_ID VARCHAR2(6)
MEMBER_ID VARCHAR2(6)
Examine this partial SQL statement:
SELECT * FROM books_transctions;
Which two WHERE conditions give the same result?
A) WHERE borrowed_date = SYSDATE AND (transaction_type= 'RM' OR member_id IN ('A101','A102'));
B) WHERE borrowed_date = SYSDATE AND transaction_type= 'RM' OR member_id IN ('A101','A102');
C) WHERE borrowed_date = SYSDATE AND (transaction_type= 'RM' AND member_id='A101' OR member_id = 'A102'));
D) WHERE (borrowed_date = SYSDATE AND transaction_type= 'RM' ) OR member_id IN ('A101','A102');
E) WHERE borrowed_date = SYSDATE AND (transaction_type= 'RM' AND ( member_id= 'A101' OR member_id = 'A102' ) );
Correct Answer: BD
那么,and和or有什么区别呢 ?
1.and表示交
2.or表示并
3.and的优先级比or高
然后我们来看下上面这个题目:(谁能一眼看出答案?)
A:表示 orrowed_date = SYSDATE and transaction_type= 'RM' 交集于 orrowed_date = SYSDATE and member_id IN ('A101','A102')
B:表示WHERE borrowed_date = SYSDATE AND transaction_type= 'RM' 交集于 member_id IN ('A101','A102');
C:表示WHERE borrowed_date = SYSDATE AND transaction_type= 'RM' AND member_id='A101' 交集于 WHERE borrowed_date = SYSDATE and member_id = 'A102'
D:这个就很明显了,前面有个括号
表示(borrowed_date = SYSDATE AND transaction_type= 'RM' )交集于 member_id IN ('A101','A102');
E:表示在member_id= 'A101' 交集于 member_id = 'A102'的结果集里面找到 borrowed_date = SYSDATE AND transaction_type= 'RM'
也就是 WHERE borrowed_date = SYSDATE AND transaction_type= 'RM' and member_id= 'A101' 交集于 WHERE borrowed_date = SYSDATE AND transaction_type= 'RM' and member_id= 'A102'
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