select = (stmt instanceof SelectStatement);
insert = (stmt instanceof InsertStatement);
update = (stmt instanceof UpdateStatement);
delete = (stmt instanceof DeleteStatement);
DMLStatement dmlStmt = (DMLStatement) stmt;
tables = dmlStmt.getTables();
// 处理生成的表达式
parseExpr(dmlStmt.getExpression(), null);
// 记录参数数目，注意: UPDATE 语句的实际参数数目要大于表达式中提取的参数数目。因此，真实地参数索引应该是:
// index = paramIndex + indexParams.size() - paramCount - 1
paramOffset = indexParams.size() - stmt.getParameterCount() - 1;
paramCount += stmt.getParameterCount();