建立主鍵（舉例）
SQL> alter table emp_ogg add constraint PK_empno primary key(empno);
--建立主鍵
查詢某表有哪些約束
SQL> desc user_constraints;
Name Null? Type
----------------------------------------- -------- ----------------------------
OWNER VARCHAR2(30)
CONSTRAINT_NAME NOT NULL VARCHAR2(30)
CONSTRAINT_TYPE VARCHAR2(1)
TABLE_NAME NOT NULL VARCHAR2(30)
SEARCH_CONDITION LONG
R_OWNER VARCHAR2(30)
R_CONSTRAINT_NAME VARCHAR2(30)
DELETE_RULE VARCHAR2(9)
STATUS VARCHAR2(8)
DEFERRABLE VARCHAR2(14)
DEFERRED VARCHAR2(9)
VALIDATED VARCHAR2(13)
GENERATED VARCHAR2(14)
BAD VARCHAR2(3)
RELY VARCHAR2(4)
LAST_CHANGE DATE
INDEX_OWNER VARCHAR2(30)
INDEX_NAME VARCHAR2(30)
INVALID VARCHAR2(7)
VIEW_RELATED VARCHAR2(14)
SQL> select CONSTRAINT_NAME,INDEX_NAME,TABLE_NAME from user_constraints;
--某使用者下，查詢約束條件
--可以查看是否存在主鍵
CONSTRAINT_NAME INDEX_NAME TABLE_NAME
------------------------------ ------------------------------ ------------------------------
PK_DEPT PK_DEPT DEPT
PK_EMP PK_EMP EMP
FK_DEPTNO EMP
SYS_C0010809 SYS_C0010809 TCUSTMER
SYS_C0010810 SYS_C0010810 TCUSTORD
