如果子查询返回0行,则标量子查询表达式的值为NULL。如果子查询返回多于一行,Oracle将返回一个错误。 You can use a scalar subquery expression in most syntax that calls for an expression (expr). In all cases, a scalar subquery must be enclosed in its own parentheses, even if its syntactic location...
前阵子总结了这篇“ORACLE当中自定义函数性优化浅析”博客,里面介绍了标量子查询缓存(scalar subquery caching),如果使用标量子查询缓存,ORACLE会将子查询结果缓存在哈希表中,如果后续的记录出现同样的值,优化器通过缓存在哈希表中的值,判断重复值不用重复调用函数,直接使用上次计算结果即可。从而减少调用函数次数,从而达...
前阵子总结了这篇“ORACLE当中自定义函数性优化浅析”博客,里面介绍了标量子查询缓存(scalar subquery caching),如果使用标量子查询缓存,ORACLE会将子查询结果缓存在哈希表中,如果后续的记录出现同样的值,优化器通过缓存在哈希表中的值,判断重复值不用重复调用函数,直接使用上次计算结果即可。从而减少调用函数次数,从而达...
You can place aScalarSubqueryanywhere anExpressionis permitted. AScalarSubqueryturns aSelectExpressionresult into a scalar value because it returns only a single row and column value. The query must evaluate to a single row with a single column. Sometimes also called an expression subquery. Syntax ...
one column value from one row. The value of the scalar subquery expression is the value of the select list item of the subquery. If the subquery returns 0 rows, then the value of the scalar subquery expression isNULL. If the subquery returns more than one row, then Oracle returns an ...
- As the basis of a function-based index - In CHECK constraints - In GROUP BY clauses - In statements that are unrelated to queries, such as CREATE PROFILE Reference:http://docs.oracle.com/cd/B28359_01/server.111/b28286/expressions013.htm...
1. 标量子查询 标量子查询(Scalar Subquery):出现在SELECT列表中的子查询称为标量子查询;内联视图(Inline View):出现在FROM … book.51cto.com|基于21个网页 2. 分级子查询 oracle认证考试中,常用单词汇总... ... retrieve data 获得数据scalar subquery分级子查询hierarchical queries 分级查询 ... ...
A method, apparatus, and stored instructions are provided for transforming an initial query having a scalar subquery with correlated predicates into a transformed query having transformed predicates that are not in the scalar subquery. The transformed predicates correspond to the correlated predicates, ...
D. A scalar subquery expression that returns zero rows evaluates to null. E. They can be used as default values for columns in a create table statement. F. They cannot be used in the values clause of an insert statement. Answer: ADF ...
If the subquery returns zero rows, the value of the scalar subquery expression is NULL. If the subquery returns multiple rows, the database returns an error. Most expressions can use a scalar subquery expression as a parameter. A scalar subquery is an invalid expression in the following cases...