and — Returns false if a value of some argument is false,
otherwise returns true.
boolean and (
val1 boolean ,
val2 boolean ,
valN boolean );
This function calculates the values of its arguments from left
to right. If the value of the calculated parameter is false, the
function returns false immediately, without calculating the
remaining parameters. If the list of arguments ends without any
false value calculated, the function returns true (thus it will
return true if called without arguments).
The name of this function is the same as the name of "and" XPATH
and XQUERY operator. Thus it must be surrounded by double quotes
when used in XPATH or XQUERY expressions. Moreover, this function
is not a part of XPATH standard, so it cannot be used if
portability is important.
Value of boolean expression argument
sequence of search operations
If two conditions must be checked, where one is simple and
another is hard to calculate, then "and" may be used to calculate
second condition only if first is true, to reduce average time of