XQuery syntax

XQuery is case-sensitive, XQuery elements, attributes, and variables must be legal XML names.

XQuery's basic grammar rules:

Some basic grammar rules:

• XQuery is case sensitive
• XQuery elements, attributes, and variables must be legal XML names.
• XQuery string value can be used single or double quotes.
• XQuery variable from "$" followed by a name and is defined, for example, $ bookstore
• XQuery comments are (: :) and segmentation, for example, (: XQuery Comment :)

XQuery conditional expression

"If-Then-Else" can be used in XQuery.

Consider the following example:

Note that the "If-Then-Else" syntax: parentheses after the if expression is required. else it is also required, but write-only "else ()" can be.

The example above results:

XQuery comparison

In XQuery, there are two ways to compare values.

1. General comparison: =, =, <, <=,>,> =!
2. Comparative values: eq, ne, lt, le, gt, ge

Compare differences between the two methods are as follows:

Consider the following XQuery expression:

If the property value q is greater than 10, the above expression returns a value of true.

The following examples, if the return is only a q, and its value is greater than 10, then the expression returns true. If more than one q is returned, an error occurs: