Where clauses

Figure 54. WhereClause


Where clauses are used for filtering (selection operator in the relational algebra).

For each incoming tuple, the expression in the where clause is evaluated to a boolean (possibly converting an atomic to a boolean). if this boolean is true, the tuple is forwarded to the next clause, otherwise it is dropped.

The following query corresponds to "SELECT series FROM captains WHERE name = 'Kathryn Janeway'".

Example 121. A where clause.

for $x in collection("captains")
where $x.name eq "Kathryn Janeway"
return $x.series

Result (run with Zorba): [ "The next generation", "Voyager" ]