Constraint for a column(1) that checks the values in another column(2) are equal to 'String1' and 'String2', setting column(1) to not null

Question

How do you create a constraint for a column(1) that checks the values in another column(2)and is equal to 'String1' and 'String2' but not 'String3', therefore setting column(1) to not null This is what I have tried so far

    Create Table ER(ERNo INTEGER,
ERSta Varchar2(8 CHAR) Default 'PENDING' Not Null,  
AUserNo Integer,
CONSTRAINT ERNoPK PRIMARY KEY(ERNO),
CONSTRAINT ERSta_check CHECK (ERSta IN ('PENDING', 'APPROVED', 'DENIED')),
CONSTRAINT AUserNoFK FOREIGN KEY (AUserNo) REFERENCES Users(UserNo),
CONSTRAINT AUserNo CHECK (WHEN (ERSta like('APPROVED')or ('DENIED')) THEN AUserNo not null);

So my question is: As AuserNo allows nulls already, How can I Set AUserNo to not null when either 'APPROVED' or 'DENIED' has been entered in ERSta?

Thanks in advance for your help.

Answer 1

check (ERSta NOT IN ('APPROVED', 'DENIED') or AUserNo is not null)

1. The check clause will be fulfilled if ERSta is another value than APPROVED/DENIED.

2. If ERSta is APPROVED or DENIED, then AUserNo must be not null.