bug fixed for sql parser OutputVisitor.

src/main/java/com/alibaba/druid/sql/ast/expr/SQLUnaryExpr.java

@@ -33,7 +33,7 @@ public class SQLUnaryExpr extends SQLExprImpl implements Serializable {
 
     public SQLUnaryExpr(SQLUnaryOperator operator, SQLExpr expr){
         this.operator = operator;
-        this.expr = expr;
+        this.setExpr(expr);
     }
 
     public SQLUnaryOperator getOperator() {
@@ -49,6 +49,9 @@ public class SQLUnaryExpr extends SQLExprImpl implements Serializable {
     }
 
     public void setExpr(SQLExpr expr) {
+        if (expr != null) {
+            expr.setParent(this);
+        }
         this.expr = expr;
     }
 

src/main/java/com/alibaba/druid/sql/dialect/mysql/visitor/MySqlOutputVisitor.java

@@ -826,7 +826,8 @@ public class MySqlOutputVisitor extends SQLASTOutputVisitor implements MySqlASTV
     @Override
     public boolean visit(MySqlIntervalExpr x) {
         print0(ucase ? "INTERVAL " : "interval ");
-        x.getValue().accept(this);
+        SQLExpr value = x.getValue();
+        value.accept(this);
         print(' ');
         print0(ucase ? x.getUnit().name() : x.getUnit().name_lcase);
         return false;

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

@@ -463,10 +463,13 @@ public class SQLExprParser extends SQLParser {
                         sqlExpr = new SQLUnaryExpr(SQLUnaryOperator.Negative, sqlExpr);
 
                         break;
-                    case QUES:
-                        sqlExpr = new SQLUnaryExpr(SQLUnaryOperator.Negative, new SQLVariantRefExpr("?"));
+                    case QUES: {
+                        SQLVariantRefExpr variantRefExpr = new SQLVariantRefExpr("?");
+                        variantRefExpr.setIndex(lexer.nextVarIndex());
+                        sqlExpr = new SQLUnaryExpr(SQLUnaryOperator.Negative, variantRefExpr);
                         lexer.nextToken();
                         break;
+                    }
                     case LPAREN:
                         lexer.nextToken();
                         sqlExpr = expr();