MySQL的describe命令

describe命令有两种格式, 一种格式和show命令的实现原理相同, 对应INFORMATION_SCHEMA中COLUMNS表.

两种格式分别如下

describe:
          describe_command table_ident
          {
            LEX *lexLex;
            mysql_init_select(lex);
            lex->current_select->parsing_placeSELECT_LIST;
            lex->sql_commandSQLCOM_SHOW_FIELDS;
            lex->select_lex.db