sql parser improved db2 support

src/main/java/com/alibaba/druid/sql/ast/SQLOver.java

@@ -25,6 +25,9 @@ public class SQLOver extends SQLObjectImpl {
     protected final List<SQLExpr> partitionBy = new ArrayList<SQLExpr>();
     protected SQLOrderBy          orderBy;
 
+    // for db2
+    protected SQLExpr             of;
+
     public SQLOver(){
 
     }
@@ -38,6 +41,7 @@ public class SQLOver extends SQLObjectImpl {
         if (visitor.visit(this)) {
             acceptChild(visitor, this.partitionBy);
             acceptChild(visitor, this.orderBy);
+            acceptChild(visitor, this.of);
         }
         visitor.endVisit(this);
     }
@@ -53,6 +57,17 @@ public class SQLOver extends SQLObjectImpl {
         this.orderBy = orderBy;
     }
 
+    public SQLExpr getOf() {
+        return of;
+    }
+
+    public void setOf(SQLExpr of) {
+        if (of != null) {
+            of.setParent(this);
+        }
+        this.of = of;
+    }
+
     public List<SQLExpr> getPartitionBy() {
         return partitionBy;
     }

src/main/java/com/alibaba/druid/sql/dialect/db2/parser/DB2Lexer.java

@@ -36,6 +36,7 @@ public class DB2Lexer extends Lexer {
         map.put("FIRST", Token.FIRST);
         map.put("ONLY", Token.ONLY);
         map.put("OPTIMIZE", Token.OPTIMIZE);
+        map.put("OF", Token.OF);
         
         DEFAULT_DB2_KEYWORDS = new Keywords(map);
     }

src/main/java/com/alibaba/druid/sql/parser/SQLExprParser.java

@@ -1036,6 +1036,12 @@ public class SQLExprParser extends SQLParser {
         }
 
         over.setOrderBy(parseOrderBy());
+        
+        if (lexer.token() == Token.OF) {
+            lexer.nextToken();
+            SQLExpr of = this.expr();
+            over.setOf(of);
+        }
 
         accept(Token.RPAREN);
         aggregateExpr.setOver(over);

src/main/java/com/alibaba/druid/sql/visitor/SQLASTOutputVisitor.java

@@ -1632,9 +1632,16 @@ public class SQLASTOutputVisitor extends SQLASTVisitorAdapter implements Printab
             printAndAccept(x.getPartitionBy(), ", ");
             print(' ');
         }
+        
         if (x.getOrderBy() != null) {
             x.getOrderBy().accept(this);
         }
+        
+        if (x.getOf() != null) {
+            print0(ucase ? " OF " : " of ");
+            x.getOf().accept(this);
+        }
+        
         print(')');
         return false;
     }