> create table t_user(id int(10) ,name varchar(32) not null,email varchar(128)); 15.2唯一性约束(unique) 作用:unique约束的字段具有唯一性,不可重复,但是可以为空(null)。 案例:修改之前的t_user表结构,把email设置为唯一性 > alter table t_user modify email varchar(128) unique; 15.3组合使用 ...
row in set (0.01 sec) How to add check constraint to an existingtable? To add a checkconstraint to an existing table the followingclause in ALTER TABLE statement is supported. ALTER TABLE <tablename> ADD [CONSTRAINT [symbol]] CHECK (condition) [[NOT] ENFORCED 1 2 ALTER TABLE ...
#约束CONSTRAINTysPRIMARYKEY(id),#主键CONSTRAINTuqUNIQUE(seat),#唯一键CONSTRAINTckCHECK(sex='男'ORsex='女'),#检查CONSTRAINTfkFOREIGNKEY(majorid)REFERENCESmajor(id)#外键,references指向主键2.添加默认约束ALTERTABLEstuinfo MODIFYCOLUMNageINTDEFAULT18;3.添加主键 #列级约束ALTERTABLEstuinfo MODIFYCOLUMNidINT...
truncate table app04news_userinfo; 报错如下: ERROR 1701 (42000): Cannot truncate a table referenced in a foreign key constraint (`platform`.`app04news_news`, CONSTRAINT `app04news_news_user_id_d2929af9_fk_app04news_userinfo_id`) 问题原因 因为数据库存在主外键关系,不能进行删除或者截断。此时...
"All tables in the MERGE table are not identically defined", #define ER_DUP_UNIQUE 1169 "Can't write, because of unique constraint, to table '%-.64s'", #define ER_BLOB_KEY_WITHOUT_LENGTH 1170 "BLOB/TEXT column '%-.64s' used in key specification without a key length", ...
..) reference_definition | ADD [CONSTRAINT [symbol]] CHECK (expr) [[NOT] ENFORCED] | DROP {CHECK | CONSTRAINT} symbol | ALTER {CHECK | CONSTRAINT} symbol [NOT] ENFORCED | ALGORITHM [=] {DEFAULT | INSTANT | INPLACE | COPY} | ALTER [COLUMN] col_name { SET DEFAULT {literal | (...
ALTER TABLE `tablename` NOCHECK CONSTRAINT `foreignkeyname`; In essence I wish to have a foreign key constraint between two tables, but want to not have it actually be enforced. Think of it as a drop-down type box filled with values from a related table, but the user is able to type...
Please MySQL implement the CHECK CONSTRAINT clause. We really need these basics before anything else. ENUM isn't a replacement for checks. Check constraints improve data quality when used correctly. Thus, the severity should be S2! Checks aren't just a fancy extension, they're vital. It's ...
Description: When a TABLE is created with a table constraint using the CHECK option, it is not reproduced when: "SHOW CREATE TABLE mytable" is called. Although I have not tested this against the Workbench product, I have a feeling the bug is present there as well. How to repeat: a) ...
ALTER TABLE table_name ADD INDEX index_name (column), ALGORITHM=INPLACE, LOCK=NONE; 遗憾的是,对于需要锁的 DDL 语句,你无法避免复制延迟。 若要减少潜在影响,请在非高峰时间(例如在晚上)执行这些类型的 DDL 操作。 降级的副本服务器 在Azure Database for MySQL 中,只读副本使用与源服务器相同的服务器...