CONSTRAINTUC_PersonUNIQUE(ID,LastName) ); SQL UNIQUE Constraint on ALTER TABLE To create aUNIQUEconstraint on the "ID" column when the table is already created, use the following SQL: MySQL / SQL Server / Oracle
UNIQUE Constraint With Alter Table We can also add theUNIQUEconstraint to an existing column using theALTER TABLEcommand. For example, For a Single Column -- add unique constraint to an existing columnALTERTABLECollegesADDUNIQUE(college_id); Here, the SQL command adds theUNIQUEconstraint to theco...
SQL UNIQUE Constraint on ALTER TABLE 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...
SQL> SELECT * FROM user_cons_columns WHERE table_name = 'TB_CONSTRAINT_3'; OWNER CONSTRAINT_NAME TABLE_NAME COLUMN_NAME POSITION --- --- --- --- --- ROBINSON SYS_C005554 TB_CONSTRAINT_3 EMAIL 1 ROBINSON PK_TB_CONS3_EMPNO_ENAME TB_CONSTRAINT_3 ENAME 2 ROBINSON PK_TB_CONS3_EMPNO...
除了创建唯一性索引外,还可以通过创建唯一性约束来添加唯一性约束。创建唯一性约束时,需要指定约束的类型为UNIQUE,并指定约束作用的列。下面是创建唯一性约束的示例代码: ALTERTABLETable_NameADDCONSTRAINTUC_Unique_ColumnsUNIQUE(Column1,Column2); 1. 2. ...
SQL> CREATE TABLE tb_constraint_1 2 ( 3 empno NUMBER PRIMARY KEY, --主键约束 4 ename VARCHAR2(20) NOT NULL, --非空约束 5 email VARCHAR2(60) UNIQUE, --唯一约束 6 sal NUMBER(5) CHECK(sal>1500), --核查约束 7 deptno NUMBER(4) REFERENCES tb_dept(deptno) --外键约束 ...
customer Non_unique: 1 Key_name idx_fk_store_id Seq_in_index: 1 Column_name: store_id Collation: A Cardinality: 2 Sub_part: NULL Packed: NULL Null: Index_type: BTREE ... *** 3. row *** Table: customer Non_unique: 1 Key_name idx_fk_address_id Seq_in_index 1 Column_name...
CREATETABLEtable_name(column_name1data_type(size)constraint_name,column_name2data_type(size)constraint_name,column_name3data_type(size)constraint_name,...); 在SQL中,有如下约束: NOT NULL:指示某列不能存储NULL值。 UNIQUE:保证某列的每行必须有唯一的值。 PRIMARY...
CREATE TABLE table_name(column_name1 data_type(size)constraint_name,column_name2 data_type(size)constraint_name,column_name3 data_type(size)constraint_name,...); 在SQL 中,我们有如下约束: NOT NULL- 指示某列不能存储 NULL 值。 UNIQUE- 保证某列的每行必须有唯一的值。 PRIMARY...
字段定义constraint约束名约否类型(字段名)-->unique,primarykey,check 字段定义constraint约否名foreingnkey(字段名)references表名(字段名)--->foreign 三、建表时约束定义 1.定义各种不同的约束 --创建一个用于作外键的表tb_dept SQL>CREATETABLEtb_dept ...