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XQuery的FLWOR语法

2009-09-11 11:30:51| 分类： dbms | 标签： |举报 |字号大中小订阅

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FLWOR（读作flower）是XQuery最重要最有特色的语法之一，
和SQL的Select-From-Where语句类似有相似的功能

FLWORExpr    ::=    (ForClause  | LetClause)+ WhereClause? OrderByClause? "return" ExprSingle 
ForClause    ::=    "for" "$" VarName TypeDeclaration? PositionalVar? "in" 
                    ExprSingle ("," "$" VarName TypeDeclaration? PositionalVar? 
                    "in" ExprSingle)* 
LetClause    ::=    "let" "$" VarName TypeDeclaration? ":=" ExprSingle
                    ("," "$" VarName TypeDeclaration? ":=" ExprSingle)*
WhereClause  ::=    "where" ExprSingle

以DB2为例

 xquery 
 for $d in db2-fn:xmlcolumn ('T.DOC') 
 let $a:=$d//title,$b:=$d/actor 
 where $a/text()='Chicago' 
 order by $b/text() 
 return $a

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