注意：如果没有模式或者使用的XQuery处理程序不知道date属性是日期类型，该语句可能会出现错误。
Note: If you don't use a schema or XQuery processor that knows that the date attribute is a date type, you can get errors with this statement.
守卫：一种编程模式。使用一些条件语句来检验和处理一些有可能导致错误的情况。
A programming pattern that USES a conditional statement to check for and handle circumstances that might cause an error.
Erlang中的模式匹配还会处理各个语句的执行流，以及从复合数据类型(元组、数组)中提取出值。
Pattern matching in Erlang also handles the execution flow of individual statements, and extracts the individual vales from compound data types (tuples, arrays).
因此，查询处理仅限于新模式文档实例，因为旧模式的所有实例计算where语句的结果都是false。
Hence, the query processing is limited to the document instances from the new schema, because all instances from previous schema evaluate the where statement as false.
正则表达式是一种非常重要和有效的字符串匹配模式，将其应用于SQL语句中，具有强大的数据处理功能。
The regular expression is a very important and effective string search mode. It has powerful data processing ability when being applied to the SQL statement.
正则表达式是一种非常重要和有效的字符串匹配模式，将其应用于SQL语句中，具有强大的数据处理功能。
The regular expression is a very important and effective string search mode. It has powerful data processing ability when being applied to the SQL statement.
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