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047-068

原创 Linux操作系统 作者:jbymy2000 时间:2012-03-18 10:15:43 0 删除 编辑
68. The following are the steps for a correlated subquery, listed in random
order:
1) The WHERE clause of the outer query is evaluated.
2) The candidate row is fetched from the table specified in the outer query.
3) The procedure is repeated for the subsequent rows of the table, till all
the rows are processed.
4) Rows are returned by the inner query, after being evaluated with the value
from the candidate row in the outer query.
Identify the option that contains the steps in the correct sequence in which
the Oracle server evaluates a correlated subquery.
A. 4, 2, 1, 3
B. 4, 1, 2, 3
C. 2, 4, 1, 3
D. 2, 1, 4, 3
Answer: C
Correlated:相互关联 evaluated:估价 candidate:候选人 process:处理
select (select t2.name from t2 where t2.did=t1.did) from t1
()里面的select t2.name from t2 where t2.did=t1.did就是inner outer
而()外面的select (select t2.name from t2 where t2.did=t1.did) from t1 就
属于outer query

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