oracle中的ALTER TABLE选项无效

Question

我遇到了oracle SQL的问题。

我的代码：

alter table kontraktai add constraint kontraktai_siuntejai_fk 
  foreign key (SIUNTEJAI_SIUNT_TEL_NR) REFERENCES siuntejai (SIUNT_TEL_NR) 
  on delete cascade;

错误：

Error starting at line : 1 in command -
alter table "kontraktai" add constraint kontraktai_siuntejai_fk foreign key (SIUNTEJAI_SIUNT_TEL_NR)
REFERENCES siuntejai SIUNT_TEL_NR on delete cascade
Error report -
SQL Error: ORA-01735: invalid ALTER TABLE option
01735. 00000 -  "invalid ALTER TABLE option"
*Cause:    
*Action:

怎么了？