constraintsoracle删除delete约束constraint oracle创建和删除约束(Oraclecreateanddeleteconstraints)Dataintegrityconstraints:creation,deletion,statementsofprimarykeys,foreignkeys,andvariousconstraintsORACLEconstraintsondatabaseintegrity:Threewaystomaintaindataintegrity:ORACLEintegrityconstraints,databasetriggers,applicationcode.ORACLE...
2 add constraint C_T_ID1 3 check (id>5) deferrable; Table altered 此时,数据字典中的情况是如下: SQL> select constraint_name, SEARCH_CONDITION cond, STATUS, DEFERRABLE, DEFERRED, VALIDATED from dba_constraints where table_name='T' and wner='SYS'; CONSTRAINT_NAME CTYPE STATUS DEFERRABLE DEFER...
When you create a primary key or unique constraint, Oracle Database will automatically create a unique index for you (assuming there isn't an index already available). In most cases you'll add the constraint to the table and let the database build the index for you....
只有唯一索引才真正提高速度,一般的索引只能提高30%左右。 Create index ename_in on emp (ename,sal); 例1:商场的商品库表结构如下,我们为该表的商品代码建立一唯一索引,使得在前台POS收款时提高查询速度。 Create table good(good_id number(8) not null, Good_desc varchar2(40), Unit_cost number(10,2...
When you create a UNIQUE constraint, Oracle creates a unique index to enforce the uniqueness of the values. Within a primary key constraint, at least one of the columns in the primary key for each row must be NOT NULL. The Primary Key ...
Function-based unique indexes can be useful in defining a conditional unique constraint on a column or combination of columns. Refer to "Using a Function-based Index to Define Conditional Uniqueness: Example" for an example. See Also: Oracle Database PL/SQL Packages and Types Reference for mor...
To enable a unique or primary key constraint, you must have the privileges necessary to create an index on the table. You need these privileges because Oracle creates an index on the columns of the unique or primary key in the schema containing the table....
CONSTRAINT s_dept_region_id_fk REFERENCES region (id), CONSTRAINT s_dept_name_region_id_uk UNIQUE(name, region_id)); 8. 较复杂的创建表例子 SQL> CREATE TABLE s_emp (id NUMBER(7) CONSTRAINT s_emp_id_pk PRIMARY KEY, last_name VARCHAR2(25) ...
Alternatively, Oracle 12 also allows to use a sequence as a default value: CREATE SEQUENCE dept_seq START WITH 1; CREATE TABLE departments ( ID NUMBER(10) DEFAULT dept_seq.nextval NOT NULL, DESCRIPTION VARCHAR2(50) NOT NULL); ALTER TABLE departments ADD ( CONSTRAINT dept_pk PRIMARY KEY (...
5. CHECK Constraint In Oracle, you can use the CHECK constraint to impose specific conditions or rules on the values stored in a column. Example: CREATETABLEStudents(Student_id NUMBERPRIMARYKEY,first_nameVARCHAR(60),last_nameVARCHAR(80),Scores NUMBER(10,2),CONSTRAINTchk_positive_ScoresCHECK(Scor...