, . , , , . .
:
1. .
2. .
3. , .
. NOT NULL.
:
ALTER TABLE Customer
ADD CONSTRAINT PK_Customer PRIMARY KEY (Cust_No);
(Unique)
. .
:
ALTER TABLE Employee
ADD CONSTRAINT Unique_Phone UNIQUE (Phone);
(Foreign keys)
. . , . .
:
ALTER TABLE Book ADD CONSTRAINT FK_Book
FOREIGN KEY (B_PubNo) REFERENCES Publisher (B_NO);
, , , . , NULL.
(Checks)
, . . .
, .
, ,
"Num" 0 4:
ALTER TABLE Property
ADD CONSTRAINT Check_Invalid_Number
CHECK (Num >= 0 AND Num <= 4);
.
SQL. SELECT. , , . .
|
|
(SELECT)
BNF-
( SELECT) . , - (BNF).
BNF :
- "::=" . , - .
- . .
- - .
- [].
- | , .
- {} , .
- "" , .
- , ".,.." , , , , . . : BNF, SQL.
- .