| 摘要 |
Techniques for effectively and efficiently supporting XML sequence type and XQuery sequence natively in a SQL system are described. According to one aspect, SQL functions that correctly handle XML sequences are provided. Thus, XML sequences are handled effectively. According to another aspect, rules for simplifying an abstract syntax tree (AST) that represents one or more such SQL functions are provided. For each such SQL function that is represented in an AST that represents a SQL query, one or more rules that are relevant to that SQL function are determined. Relevant rules are applied to the representation of the SQL function within the AST. Through the application of the rules to the representations of the SQL functions within the AST, the AST is modified in a manner that simplifies the AST prior to the evaluation of the AST at query execution time. Thus, XML sequences are handled efficiently.
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