select ... for update [nowait] 行锁，直到该语句的事务被commit语句或rollback语句结束为止；

select ... for update nowait语句将要更改的数据试探性地加锁，就可以通过立即返回的错误提示而明白其中的原因。

查询ORACLE锁了哪张卡：
SELECT S.SID SESSION_ID, S.USERNAME, DECODE(LMODE, 0, 'None', 1, 'Null', 2, 'Row-S (SS)', 3, 'Row-X (SX)', 4, 'Share', 5, 'S/Row-X (SSX)', 6,

'Exclusive', TO_CHAR(LMODE)) MODE_HELD, DECODE(REQUEST, 0, 'None', 1, 'Null', 2, 'Row-S (SS)', 3, 'Row-X (SX)', 4, 'Share', 5, 'S/Row-X (SSX)', 6,

'Exclusive', TO_CHAR(REQUEST)) MODE_REQUESTED, O.OWNER||'.'||O.OBJECT_NAME||' ('||O.OBJECT_TYPE||')', S.TYPE LOCK_TYPE, L.ID1 LOCK_ID1, L.ID2 LOCK_ID2

FROM V$LOCK L, SYS.DBA_OBJECTS O, V$SESSION S WHERE L.SID = S.SID AND L.ID1 = O.OBJECT_ID;

直接用ROWID替代WHERE CURRENT OF YOUR_CURSOR_NAME语句，
尤其在相对繁习的程序里头。

COMMIT必需存在程序结尾。以防死锁成形。

EXCEPTION里的ROLLBACK是最基本的需要。

例子：

declare
-- query emp.name
cursor cur_emp
is
select a.deptno,
a.dname,
a.rowid,
b.rowid rowid_1
from dept a, emp b
where empno = 7369
and a.deptno = b.deptno
for update nowait;

-- local variables
v_deptno dept.deptno%type;
v_dname dept.dname%type;
v_rowid rowid;
v_rowid_1 rowid;

begin
open cur_emp;
loop
fetch cur_emp into v_deptno, v_dname, v_rowid, v_rowid_1;
exit when cur_emp%notfound;

update dept
set dname = 'abc'
where rowid = v_rowid;

update emp
set ename = 'frank'
where rowid = v_rowid_1;

end loop;
close cur_emp;
commit;
exception
when others then
rollback;
raise;
end;