编写XQuery函数调用序列：如何避免冗余let $tmp赋值语句

你当前的代码里用大量let $tmp :=来包裹trace、sql:execute这类副作用操作，本质是为了满足FLOWR表达式的语法要求——FLOWR只能包含for/let/where/order by/return子句，不能直接裸写执行语句。以下是几种无需冗余赋值的实现方式：

1. 标准XQuery方案：用序列表达式组织操作 #

直接把所有需要执行的操作放在return的序列中，XQuery会按顺序执行序列里的每个子表达式，忽略它们的返回值（或合并成空序列），完全符合语法要求：

declare function module:import($xmlsrc as xs:string, $conn as xs:anyURI) {
  let $root := module:getXml($xmlsrc)
  return (
    (: 处理Table01 :)
    trace("Table01"),
    sql:execute($conn, "insert into Table01 (rel1,rel2,rel3,rel4,rel5) values(" 
         || 2 || ", 
      '" || $root//myns:ftr[@n='abc']/myns:ftr[@type='p1'] || "', 
      '" || $root//myns:ftr[@n='abc']/myns:ftr[@type='p2'] || "', 
      '" || $root//myns:ftr[@n='abc']/myns:ftr[@type='p3'] || "', 
      '" || $root//myns:ftr[@n='abc']/myns:ftr[@type='p4'] || "')"),
    
    (: 处理Table02 :)
    sql:execute($conn, "insert into Table02 (rel1,rel2,rel3,rel4,rel5) values(" 
         || 3 || ", 
      '" || $root//myns:div[@n='abc']/myns:xyz[@type='p5'] || "', 
      '" || $root//myns:div[@n='abc']/myns:xyz[@type='p6'] || "', 
      '" || $root//myns:div[@n='abc']/myns:xyz[@type='p7'] || "', 
      '" || $root//myns:div[@n='abc']/myns:xyz[@type='p8'] || "')"),
    
    (: 更多表操作 :)
    ()
  )
};

2. 扩展语法方案：使用do语句（需处理器支持） #

部分XQuery处理器（如支持XQuery Update Facility或扩展语法的）提供do { ... }语法，专门用于执行副作用操作，无需绑定变量：

declare function module:import($xmlsrc as xs:string, $conn as xs:anyURI) {
  let $root := module:getXml($xmlsrc)
  return (
    do { trace("Table01") },
    do { sql:execute($conn, "insert into Table01 (rel1,rel2,rel3,rel4,rel5) values(" 
         || 2 || ", 
      '" || $root//myns:ftr[@n='abc']/myns:ftr[@type='p1'] || "', 
      '" || $root//myns:ftr[@n='abc']/myns:ftr[@type='p2'] || "', 
      '" || $root//myns:ftr[@n='abc']/myns:ftr[@type='p3'] || "', 
      '" || $root//myns:ftr[@n='abc']/myns:ftr[@type='p4'] || "')") },
    do { sql:execute($conn, "insert into Table02 ...") }
  )
};

注意：do不是标准XQuery 1.0语法，使用前需确认你的处理器支持该扩展。

3. 优化方案：封装重复逻辑为子函数 #

如果有大量类似的SQL插入操作，建议把SQL拼接和执行逻辑封装成子函数，既消除冗余赋值，又提升代码可维护性：

declare function module:insert-table($conn as xs:anyURI, $table-name as xs:string, $id as xs:integer, $column-values as xs:string*) {
  let $sql := concat(
    "insert into ", $table-name, " (rel1,rel2,rel3,rel4,rel5) values(",
    $id, ", '", string-join($column-values, "', '"), "')"
  )
  return sql:execute($conn, $sql)
};

declare function module:import($xmlsrc as xs:string, $conn as xs:anyURI) {
  let $root := module:getXml($xmlsrc)
  return (
    trace("Table01"),
    module:insert-table(
      $conn, "Table01", 2,
      ($root//myns:ftr[@n='abc']/myns:ftr[@type='p1'],
       $root//myns:ftr[@n='abc']/myns:ftr[@type='p2'],
       $root//myns:ftr[@n='abc']/myns:ftr[@type='p3'],
       $root//myns:ftr[@n='abc']/myns:ftr[@type='p4'])
    ),
    module:insert-table(
      $conn, "Table02", 3,
      ($root//myns:div[@n='abc']/myns:xyz[@type='p5'],
       $root//myns:div[@n='abc']/myns:xyz[@type='p6'],
       $root//myns:div[@n='abc']/myns:xyz[@type='p7'],
       $root//myns:div[@n='abc']/myns:xyz[@type='p8'])
    )
  )
};

内容的提问来源于stack exchange，提问作者user18451290