Not exists:MySQL能够对查询进行LEFT JOIN优化,发现1个匹配LEFT JOIN标准的行后,不再为前面的的行组合在该表内检查更多的行。 range checked for each record (index map: #):MySQL没有发现好的可以使用的索引,但发现如果来自前面的表的列值已知,可能部分索引可以使用。 Using file
1 row in set (0.0 2 sec)四、判断字段是否存在 mysql_connect('localhost', 'root', 'root');mysql_select_db('demo');$test = mysql_query('Describe cdb_posts first');$test = mysql_fetch_array($test);$test[0]返回的是该字段的名称,⽐如我要查询first字段,返回的就是first 如果此字段不...
mysql> alter table employee drop foreign key fk_emp_dept; Query OK, 0 rows affected (0.22 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> drop table department; Query OK, 0 rows affected (0.04 sec) mysql> show tables; +---+ | Tables_in_rm_tab | +---+ | employee | +---+ ...
version 9.0 MySQL 9.0 Reference Manual/.../DESCRIBE Statement 15.8.1 DESCRIBE Statement TheDESCRIBEandEXPLAINstatements are synonyms, used either to obtain information about table structure or query execution plans. For more information, seeSection 15.7.7.6, “SHOW COLUMNS Statement”, andSection 15.8...
mysql_connect(localhost, root, root); mysql__db(demo); $test = mysql_query(Describe cdb_posts first); $test = mysql_fetch_array($test); $test[0]返回的是该字段的名称,比如我要查询first字段,返回的就是first 如果此字段不存在返回的就是NULL,通过这样可以判断一个字段是否存在 ...
Account.QueryError Instance %s query account error 实例%s查询帐户错误 400Connect.Timeout Service can not connect to instance temporarily. 服务无法连接到实例 404InvalidDBCluster.NotFound The DBClusterId provided does not exist in our records. 当前记录中不存在提供的DBClusterId。 404InvalidDB...
400 InvalidBackupSet The specified database does not exist in the backup set. 备份集中没有指定的数据库。 400 OrdTCommodityQueryError Failed to query for product. 查询产品失败。 400 ProductInstanceReleased The instance has been released. Please check before placing the order. 实例已释放,请核实后下...
mysql> CREATE TABLE employee (-> ID INT(2) auto_increment primary key,-> First_name VARCHAR(20),-> Last_name VARCHAR(30),-> Start_date DATE,-> Salary int(6),-> city VARCHAR(20),-> description VARCHAR(20)-> );Query OK, 0 rows affected (0.02 sec)mysql> ...
Bug #251 DESCRIBE on a query with a grouped subquery crashes mysql Submitted: 8 Apr 2003 12:50Modified: 13 Jun 2003 14:07 Reporter: Daniel Penning Email Updates: Status: Closed Impact on me: None Category: MySQL ServerSeverity: S2 (Serious) Version: 4.1.0OS: Any (All) Assigned to:...
1、 S3（Simple Storage Service） a) 对象存储服务 b) 存储任意类型文件 c) 存储桶：...