oracle的约束
* 如果某个约束只作用于单独的字段，即可以在字段级定义约束，也可以在表级定义约束，但如果某个约束作用于多个字段，
必须在表级定义约束
* 在定义约束时可以通过constraint关键字为约束命名，如果没有指定，oracle将自动为约束建立默认的名称
定义primary key约束(单个字段）
create table employees (empno number(5) primary key,...)
sql> sql> create table emp (empno number(4) not null, 2 ename varchar2(10), 3 job varchar2(9), 4 mgr number(4), 5 hiredate date, 6 sal number(7, 2), 7 comm number(7, 2), 8 deptno number(2)); table created. sql> sql> insert into emp values (7369, 'smith', 'clerk', 7902, to_date('17-dec-1980', 'dd-mon-yyyy'), 800, null, 20); 1 row created. sql> insert into emp values (7499, 'allen', 'salesman', 7698, to_date('20-feb-1981', 'dd-mon-yyyy'), 1600, 300, 30); 1 row created. sql> insert into emp values (7521, 'ward', 'salesman', 7698, to_date('22-feb-1981', 'dd-mon-yyyy'), 1250, 500, 30); 1 row created. sql> insert into emp values (7566, 'jones', 'manager', 7839, to_date('2-apr-1981', 'dd-mon-yyyy'), 2975, null, 20); 1 row created. sql> insert into emp values (7654, 'martin', 'salesman', 7698,to_date('28-sep-1981', 'dd-mon-yyyy'), 1250, 1400, 30); 1 row created. sql> insert into emp values (7698, 'blake', 'manager', 7839,to_date('1-may-1981', 'dd-mon-yyyy'), 2850, null, 30); 1 row created. sql> insert into emp values (7782, 'clark', 'manager', 7839,to_date('9-jun-1981', 'dd-mon-yyyy'), 2450, null, 10); 1 row created. sql> insert into emp values (7788, 'scott', 'analyst', 7566,to_date('09-dec-1982', 'dd-mon-yyyy'), 3000, null, 20); 1 row created. sql> insert into emp values (7839, 'king', 'president', null,to_date('17-nov-1981', 'dd-mon-yyyy'), 5000, null, 10); 1 row created. sql> insert into emp values (7844, 'turner', 'salesman', 7698,to_date('8-sep-1981', 'dd-mon-yyyy'), 1500, 0, 30); 1 row created. sql> insert into emp values (7876, 'adams', 'clerk', 7788,to_date('12-jan-1983', 'dd-mon-yyyy'), 1100, null, 20); 1 row created. sql> insert into emp values (7900, 'james', 'clerk', 7698,to_date('3-dec-1981', 'dd-mon-yyyy'), 950, null, 30); 1 row created. sql> insert into emp values (7902, 'ford', 'analyst', 7566,to_date('3-dec-1981', 'dd-mon-yyyy'), 3000, null, 20); 1 row created. sql> insert into emp values (7934, 'miller', 'clerk', 7782,to_date('23-jan-1982', 'dd-mon-yyyy'), 1300, null, 10); 1 row created. sql> sql> * from emp; empno ename job mgr hiredate sal comm deptno ---------- ---------- --------- ---------- --------- ---------- ---------- ---------- 7369 smith clerk 7902 17-dec-80 800 20 7499 allen salesman 7698 20-feb-81 1600 300 30 7521 ward salesman 7698 22-feb-81 1250 500 30 7566 jones manager 7839 02-apr-81 2975 20 7654 martin salesman 7698 28-sep-81 1250 1400 30 7698 blake manager 7839 01-may-81 2850 30 7782 clark manager 7839 09-jun-81 2450 10 7788 scott analyst 7566 09-dec-82 3000 20 7839 king president 17-nov-81 5000 10 7844 turner salesman 7698 08-sep-81 1500 0 30 7876 adams clerk 7788 12-jan-83 1100 20 empno ename job mgr hiredate sal comm deptno ---------- ---------- --------- ---------- --------- ---------- ---------- ---------- 7900 james clerk 7698 03-dec-81 950 30 7902 ford analyst 7566 03-dec-81 3000 20 7934 miller clerk 7782 23-jan-82 1300 10 14 rows selected. sql> sql> alter table emp 2 add ( 3 gender varchar(10)); table altered. sql> sql> alter table emp 2 add constraint ck_gender 3 check (gender in ('male', 'female')); table altered. sql> sql> update emp set gender = 'male' where mod(empno,2) = 0; 10 rows updated. sql> sql> select * from emp; empno ename job mgr hiredate sal comm deptno gender ---------- ---------- --------- ---------- --------- ---------- ---------- ---------- ---------- 7369 smith clerk 7902 17-dec-80 800 20 7499 allen salesman 7698 20-feb-81 1600 300 30 7521 ward salesman 7698 22-feb-81 1250 500 30 7566 jones manager 7839 02-apr-81 2975 20 male 7654 martin salesman 7698 28-sep-81 1250 1400 30 male 7698 blake manager 7839 01-may-81 2850 30 male 7782 clark manager 7839 09-jun-81 2450 10 male 7788 scott analyst 7566 09-dec-82 3000 20 male 7839 king president 17-nov-81 5000 10 7844 turner salesman 7698 08-sep-81 1500 0 30 male 7876 adams clerk 7788 12-jan-83 1100 20 male empno ename job mgr hiredate sal comm deptno gender ---------- ---------- --------- ---------- --------- ---------- ---------- ---------- ---------- 7900 james clerk 7698 03-dec-81 950 30 male 7902 ford analyst 7566 03-dec-81 3000 20 male 7934 miller clerk 7782 23-jan-82 1300 10 male 14 rows selected. sql> sql> update emp set gender = 'female' where mod(empno,2) = 1; 4 rows updated. sql> sql> select ename, job, gender from emp order by gender, ename; ename job gender ---------- --------- ---------- allen salesman female king president female smith clerk female ward salesman female adams clerk male blake manager male clark manager male ford analyst male james clerk male jones manager male martin salesman male ename job gender ---------- --------- ---------- miller clerk male scott analyst male turner salesman male 14 rows selected. sql> sql> insert into emp (empno, ename, gender) values (8001, 'pat', 'unknown'); insert into emp (empno, ename, gender) values (8001, 'pat', 'unknown') * error at line 1: ora-02290: check constraint (sys.ck_gender) violated sql> sql> drop table emp; table dropped.
