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# XQuery Syntax * * * XQuery is case-sensitive, and XQuery elements, attributes, and variables must be valid XML names. * * * ## Basic XQuery Syntax Rules: Some basic syntax rules: * XQuery is case-sensitive * XQuery elements, attributes, and variables must be valid XML names. * XQuery string values can use single or double quotes. * XQuery variables are defined by "$" followed by a name, for example, $bookstore * XQuery comments are delimited by (: and :), for example, (: XQuery comment :) * * * ## XQuery Conditional Expressions "If-Then-Else" can be used in XQuery. See the following example: for $x in doc("books.xml")/bookstore/book return if ($x/@category="CHILDREN") then{data($x/title)} else{data($x/title)} Note the syntax of "If-Then-Else": The parentheses after the if expression are required. The else is also required, but you can just write "else ()". The result of the above example: Everyday Italian Harry Potter Learning XML XQuery Kick Start * * * ## XQuery Comparisons In XQuery, there are two ways to compare values. 1. General comparisons: =, !=, <, , >= 2. Value comparisons: eq, ne, lt, le, gt, ge ### The differences between these two comparison methods are as follows: See the following XQuery expression: $bookstore//book/@q > 10 If the value of the q attribute is greater than 10, the expression above returns true. As in the following example, if only one q is returned and its value is greater than 10, the expression returns true. If more than one q is returned, an error occurs: $bookstore//book/@q gt 10 AI is thinking... [](#)(#) (#)[](#) [ByteArk Coding Plan supports Doubao, GLM, DeepSeek, Kimi, MiniMax and other mainstream large models, official direct supply stable and reliable. ¥9.9/month Activate now](https://maas.xfyun.cn/modelSquare?ch=maas_lm_l2E)