047 the steps for a correlated subquery
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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
1) The WHERE clause of the outer query is evaluated.
外查询的where子句来开始评估
2) The candidate row is fetched from the table specified in the outer query.
外查询从表中取出候选行
3) The procedure is repeated for the subsequent rows of the table, till all the rows are processed.
表中随后的列也重复这一过程,直到所有的列都被处理
4) Rows are returned by the inner query, after being evaluated with the value from the candidate row in the outer query.
外查询的值传到内查询中,内部查询用这个值进行自己查询的评估之后,得到的列被内查询返回到外查询
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