| ALTER COLUMN <列名> { SET DEFAULT <默认值> | DROP DEFAULT } | MODIFY COLUMN <列名> <类型> | DROP COLUMN <列名> | RENAME TO <新表名> | CHARACTER SET <字符集名> | COLLATE <校对规则名> } (1)修改表名 MySQL 通过 ALTER TABLE 语句来实现表名的修改,语法规则如下: ALTER TABLE <旧...
MySQL8.0.12中DDL新增instant语法,只修改元数据,不需要锁表,这里最重要的改进是add column instant(即刻加列),在8.0之前版本,Online DDL下,加字段可以使用inplace方式,虽然不会长时间阻塞写入,但其实还是需要rebuild重构表,这有几个负作用: 1. 对于大表,变更时间长 2. 需要额外的磁盘空间 3. 会消耗大量的CPU,...
UPDATE t_student SET valueName_1 = newVAl,valueName_2 = newVal WHERE condition1 && condition2 --全部对所有数值全部改完 UPDATE t_student SET valueName_1 = newVal ,valueName_2= newVal; 1. 2. 3. 4. 5. 6. 查 --查询表所有数据 SELECT * FROM t_student; -- 查询指定列 SELECT val...
• The BINARY attribute is a nonstandard MySQL extension that is shorthand for specifying the binary (_bin) collation of the column character set (or of the table default character set if no column character set is specified). In this case, comparison and sorting are based on numeric charac...
VALUES(@@identity,’some value’) 如果表mytable有一个标识字段,该字段的值会插入表anothertable的another_first字段。这是因为变量@@identity总是保存最后一次插入标识字段的值。 字段another_first应该与字段first_column有相同的数据类型。但是,字段another_first不能是应该标识字段。Another_first字段用来保存字段firs...
单表:又名Noshard表,即无需拆分,且没有做任何特殊处理的表,目前分布式实例将该表默认存放在第一个物理节点组(set)中。 广播表:又名小表广播技术,即设置为广播表后,该表的所有操作都将广播到所有物理节点组(set)中,每个SET都有该表的全量数据,常用于业务系统的配置表等。值得...
--echo Another sql_mode test echo should return only 1 row; query_get_value 语法: query_get_value(query, col_name, row_num) 获得query 返回的结果中某行某列的值。 示例: 假如.test 文件内容如下: CREATE TABLE t1(a INT, b VARCHAR(255), c DATETIME); SHOW COLUMNS FROM t1; let $value...
If set to 0, there is no limit to the number of queued connection requests. (Default: 0) Pool events acquire The pool will emit an acquire event when a connection is acquired from the pool. This is called after all acquiring activity has been performed on the connection, right before ...
帮助中心 >产品文档 >数据库 >相关技术支持 >mysql出错的代码解析及解答 1005:创建表失败 1006:创建数据库失败 1007:数据库已存在,创建数据库失败 1008:数据库不存在,删除数据库失败 1009:不能删除数据库文件导致删除数据库失败 1010:不能删除数据目录导致删除数据库失败 ...
An auto-increment column is also a good choice if there is any doubt whether the value of the primary key column could ever change. Changing the value of a primary key column is an expensive operation, possibly involving rearranging data within the table and within each secondary index. ...