Answer Posted / anil

ANS:
COLUMN LEVEL CONSTRAINT
If we provide constraint along with column while creating the table then it is column level constraint. For column level constraint a constraint name is not mandatory.

TABLE(ROW) LEVEL CONSTRAINT
If we provide constraint after providing all the columns then it is table level constraint.For table level constraint a constraint name is mandatory.

Advantage of table level constraint:
We can create composite PK and composite FK in table level constraints but we cant create these in column level constraints.

Example:
CREATE TABLE oracle_tab
(
ord_id  NUMBER,
pid NUMBER,
qty NUMBER(2),
ord_dt DATE NOT NULL, /*column level constraint(cant be created as table level constraint)*/
price NUMBER(9,1) DEFAULT 0, /*column level constraint(cant be created as table level constraint)*/
CONSTRAINT ord_pk PRIMARY KEY(ord_id,pid), /*table level(can be created either as table level constraint or column level)*/
CONSTRAINT ord_fk FOREIGN KEY(pid) REFERENCES products(pid),/*table level(can be created either as table level constraint or column level)*/
CONSTRAINT ord_ch CHECK(qty>0) /*table level(can be created either as table level constraint or column level)*/
);

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