terms in db

原创于 2015-04-18 12:35:34 发布 · 291 阅读

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本文介绍了SQL中相关子查询的概念及使用规则，包括如何在where子句中使用来自外层查询的相关名称，以及相关查询作用域规则等内容。

                    
                    correlated subquery(相关子查询) 

correlation name from an outer query used in a subquery in a where clause 

scoping rule for correlation query 

1)It’s only legal to use correlation names defined in the subquery itself or in any query that contains the subquery. 

2)If a correlation is defined both locally and globally, then local correlation applies. (analogous to the scoping rule of programming languages)