code: private void generateExistsClause(IntrospectedTable introspectedTable, XmlElement element, List<Element> values) {
          element.addElement(new TextElement("select"));
  
          for (Element value : values) {
              element.addElement(value);
          }
  
          element.addElement(new TextElement("from dual where not exists"));
          element.addElement(new TextElement("("));
          element.addElement(new TextElement("select 1 from " + introspectedTable.getFullyQualifiedTableNameAtRuntime()));
  
          // if example
          element.addElement(XmlElementGeneratorTools.getUpdateByExampleIncludeElement(introspectedTable));
  
          element.addElement(new TextElement(")"));
      }
docs: exists 语句
  +635
  @param introspectedTable
  @param element
  @param values