Examples of org.apache.derby.impl.sql.compile.SubqueryNode

org.apache.derby.impl.sql.compile.SubqueryNode

A SubqueryNode represents a subquery. Subqueries return values to their outer queries. An quantified subquery is one that appears under a quantified operator (like IN or EXISTS) - quantified subqueries can return more than one value per invocation. An expression subquery is one that is not directly under a quantified operator - expression subqueries are allowed to return at most one value per invocation (returning no value is considered to be equivalent to returning NULL). There are a large number of subquery types. Because of the large number of types, and the large amount of shared code, we have decided to have 1 SubqueryNode without any subclasses. The subquery type (and operator) is encoded in the subqueryType field. The query optimizer is responsible for optimizing subqueries, and also for transforming them so that code can be generated for them. The optimizer may eliminate some subqueries by transforming them into joins, or it may change the internal form of a subquery (for example, transforming 'where x in (select y from z where ...)' into 'where (select true from z where x = y and ...)'). Note that aggregates present some additional issues. A transformation such as:

expression

has to be treated specially if expression has an aggregate. We change it to:

where x = (SELECT true FROM (SELECT MAX(x) FROM z) WHERE SQLCOL1 = y) @author Jeff Lichtman


/*
 * <A NAME="derivedTable">derivedTable</A>
 */
  final public ResultSetNode derivedTable() throws ParseException, StandardException {
        SubqueryNode tableSubquery;
    jj_consume_token(LEFT_PAREN);
    tableSubquery = tableSubquery(SubqueryNode.FROM_SUBQUERY, null);
    jj_consume_token(RIGHT_PAREN);
                {if (true) return tableSubquery.getResultSet();}
    throw new Error("Missing return statement in function");
  }

Examples of org.apache.derby.impl.sql.compile.SubqueryNode

Related Classes of org.apache.derby.impl.sql.compile.SubqueryNode