任何函数的返回值都是子句(在我们的示例中只有一行)中最后一个表达式的结果。
The return value of any function is the result of the last expression in that clause (in our examples there is only one line).
给定数据库行中的指定列值集合可以在一个或多个同步处理的XPath表达式中引用。
A collection of named column values from a located database row are referenced within one or more synchronously processed XPath expressions.
第一个表达式必须为串联的行值。
The first expression must be the row value that must be concatenated
对于DatabaseRoute节点，始终是结果集第一行中的指定列值被引用，并用于这些xpath路由表达式。
For the DatabaseRoute node it is always the named column values located in the first row within the result set that are referenced and acted upon in these XPath routing expressions.
可以在sql语句的where子句中使用它只选择那些对于XPath表达式返回非空xml值的行。
It can be used in the WHERE clause of an SQL statement to select only the rows that return non-trivial XML values for the XPath expression.
第14行中表达式的第一部分用来检查none值。
The first part of the expression in Line 14 is used to check for a value of None.
与把值分配给不同变量而将表达式分成多行相比较，将一个表达式放在一行上看着更整齐时。
When an expression looks cleaner on one line, rather than split into multiple lines by assigning values to different variables.
where子句包含由OR操作符联结的两个表达式，这意味着对于特定行，如果任一表达式值为TRUE，则将删除该行。
The WHERE clause contains two expressions that are joined by the or operator, which means that if either expression evaluates as TRUE for a specific row, that row will be deleted.
这可以通过包含行修改时间戳列的表实现，通过定义行修改时间戳列来保存ROWCHANGETIMESTAMP表达式生成的时间戳值。
This is implemented by a table containing a row change timestamp column defined to store the timestamp values generated by a ROW CHANGE TIMESTAMP expression.
表具有一个行修改时间戳列：ROWCHANGETOKEN表达式返回一个从列的时间戳值获得的bigint值。
The table has a row change timestamp column: a row change TOKEN expression returns a BIGINT value derived from the timestamp value in the column.
这些元素包含col - spec元素，后者的select属性规定了，对应于xml源文档中当前的行元素，将使用何种表达式来计算每个行值。
These elements contain col-spec elements whose select attribute specifies, relative to the current row element from the XML source, what expressions are used for each row value.
这是因为XMLQUERY函数中的XQuery表达式每次应用于一行(文档)，并不会从结果集中去掉一行，只是修改它的值。
This is because the XQuery expression in the XMLQUERY function is applied to one row (document) at a time and never removes a row from the result set, only modifies its value.
布尔表达式的设计意图就是表达运行时值为表达式时值意图真或假的属性，在某个时刻判断此属性的值就可以决定执时刻可以决定行是否继续。
Boolean expressions are intended precisely to express background contract express runtime true or false properties-properties that at any point in the execution may hold or not hold.
布尔表达式的设计意图就是表达运行时值为表达式时值意图真或假的属性，在某个时刻判断此属性的值就可以决定执时刻可以决定行是否继续。
Boolean expressions are intended precisely to express background contract express runtime true or false properties-properties that at any point in the execution may hold or not hold.
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