不能用在check约束中 Scalar Subquery Expressions A scalar subquery expression is a subquery that returns exactly 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 ...
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 already positions it within parentheses (for example, when the scalar subquery is used as the ...
ScalarSubquery 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 su...
- As hash expressions for clusters - In the RETURNING clause of DML statements - 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/serve...
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...
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...
which three are true about scalar subquery expressions? A. They cannot be used in group by clauses. B. A scalar subquery expression that returns zero rows evaluates to zero. C. They can be nested. D. A scalar subquery expression that returns zero rows evaluates to null. ...
Which two are true about scalar subquery expressions?; You cannot correlate them with a table in the parent statement; You can use them as a default value for a column; You must enclose them in parentheses; They can return at most one row;E They can retu