-- add unique constraint to multiple columnsALTERTABLECollegesADDUNIQUEUnique_College (college_id, college_code); Here, the SQL command adds theUNIQUEconstraint tocollege_idandcollege_codecolumns in the existingCollegestable. Also,Unique_Collegeis a name given to theUNIQUEconstraint defined forcollege_...
To create a UNIQUE constraint on the "P_Id" column when the table is already created, use the following SQL: MySQL / SQL Server / Oracle / MS Access: ALTERTABLEPersonsADDUNIQUE(P_Id) To allow naming of a UNIQUE constraint, and for defining a UNIQUE constraint on multiple columns, use ...
SQL UNIQUE Constraint on CREATE TABLE The following SQL creates aUNIQUEconstraint on the "ID" column when the "Persons" table is created: SQL Server / Oracle / MS Access: CREATETABLEPersons ( ID intNOTNULLUNIQUE, LastName varchar(255)NOTNULL, ...
You can create a unique constraint in SQL Server by using SQL Server Management Studio or Transact-SQL to ensure no duplicate values are entered in specific columns that don't participate in a primary key. Creating a unique constraint automatically creates a corresponding unique index....
一、UNIQUE CONSTRAINT IN DATABASES 在数据库中,约束条件是用来限制所插入数据库中的数据类型、数量以及数据之间的关系等。其中,unique约束是一种常见的约束类型,它主要用于保证一个表中的一列或者是多列的组合值是唯一的。一旦这种约束被定义,任何试图插入重复值的操作都会被数据库系统拒绝。这种功能在处理那些需要唯...
1、使用sql查询主键的唯一约束当前最大值：select max（id） from table；（id为number类型）select max（to_number(id)） from table;(id为非number类型)2、使用sql查询该表的序列的下一个值 select SEQ.NEXTVAL from dual;（seq是对应表的序列名）3、最后使用PL/SQL客户端编辑序列，将序列的下一...
test=#altertabletbl_uniqueaddconstraintuk_tbl_unique_a_bunique(a,b);ALTERTABLE 如果表中没有主键或NOT NULL的唯一键,那么可以利用表的OID属性,将表的oid列显示出来,该列类似主键的功能。利用该列,可以将重复数据删除到只剩一条,先使用下面的SQL语句,修改表的属性。
ALTER TABLE ADD CONSTRAINT UNIQUE(); 实例2,修改数据表 demo_department,指定部门的名称唯一,输入的 SQL 语句和运行结果如下所示。 mysql> ALTER TABLE demo_department -> ADD CONSTRAINT unique_name UNIQUE(name); Query OK, 0 rows affected (0.63 sec) ...
constraint fk_info1_depart1 foreign key (depart_id) references depart1(id) ) default charset=utf8; -- 如果表结构创建好了,额外添加外键 alter table info add constraint fk_info_depart foreign key info(depart_id) references depart(id);
occurs if you change the transaction isolation level toREAD COMMITTEDor enable theinnodb_locks_unsafe_for_binlogsystem variable (which is now deprecated). In this case, gap locking is disabled for searches and index scans and is used only for foreign-key constraint checking and duplicate-key ...