清单6创建一个标量函数，它从输入文档中提取出一个特定的xml元素。然后，在一个简单的SQL查询中调用此函数，从而返回给定的客户的姓名。
Listing 6 creates a scalar function that extracts a given XML element from an input document and shows how this function can be invoked in a simple SQL query to return the name of a given customer.
SHIP3操作符包含一个语句，该语句表明标量子查询的结果放在一个主机变量中。
The SHIP3 operator contains the statement that shows the result of the scalar subquery being bound in as a host variable.
标量子查询是一种嵌入式查询，返回包含单个列的单个行，本质上就是单个值，该值称为标量。
A scalar subquery is an embedded query that returns a single row that contains a single column — essentially, a single value, which is known as a scalar.
与SHIP1操作符相关的语句表明该标量子查询在Oracle上计算。
The statement associated with the SHIP1 operator shows the scalar subquery being computed on Oracle.
首先需要将标量子查询的结果传送到联邦服务器。
The result of the scalar subquery first needs to be transferred to the federated server.
两种查询可以用于update语句的where子句中：标量子查询和表子查询。
Two types of queries can be used in the WHERE clause of an UPDATE statement: a scalar subquery and a table subquery.
可以使用标量子查询选择将用于where子句的表达式中的特定值。
You can use a scalar subquery to select a specific value that will be used in the expression of the WHERE clause.
清单2显示具有4个元素的阵列构造函数，其值分别由NULL常数、变量、文字和标量子查询提供。
Listing 2 shows an array constructor with four elements with values given by the NULL constant, a variable, a literal and a scalar sub-query, respectively.
在此上下文中不允许使用子查询。只允许使用标量表达式。
Subqueries are not allowed in this context. Only scalar expressions are allowed.
在此上下文中不允许使用子查询。只允许使用标量表达式。
Subqueries are not allowed in this context. Only scalar expressions are allowed.
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