Some basic syntax rules:

• XQuery is case-sensitive one
• XQuery elements, attributes, and variables must have valid XML names
• An XQuery string value can be in the single or double quotes
• An XQuery variable is defined with a $ sign followed by a name, e.g. $bookstore
• XQuery comments are always delimited by (: and :), e.g. (: XQuery Comment :)

"If-Then-Else" expression are allowed in XQuery.

Look at the example which is given below:

Notes on the "if-then-else" syntax: parentheses around the if expression are always required. else is required, but it can be just else ().

The result of an example above will be:

There are two ways of comparing values are available in XQuery.
1. General comparisons: =, !=, >, >=, <, <=
2. Value comparisons: eq, ne, gt, ge,lt,le,
The difference between the two comparison methods are given below. Look at the XQuery expressions which is given below: