Oracle 1Z0-071, SQL Constraints

Unique Constraints

Requires data in the column to be unique, multiple nulls are allowed. When used in conjunction with NOT NULL, it is effectively identical to a PRIMARY KEY.

Cannot be applied to UNIQUE constraint on a column of TIMESTAMP WITH TIME ZONE , CLOB or BLOB datatype.

Primary Key

May be applied to more than one column, however a table may only have one primary key.

Cannot be applied to TIMESTAMP WITH TIME ZONE, CLOB, or BLOB data types. Due to the size of LOB data types, indexing is not rational.

Foreign Key

Requires that the referenced table’s column have a unique constraint only. A PRIMARY KEY constraint would satisfy this requirement, being the combination of UNIQUE and NOT NULL

Cannot be applied to TIMESTAMP WITH TIME ZONE , CLOB, or BLOB data types.

Check

Requires a column to comply with a specific condition.

Cannot be applied to the Date datatype.

Not Null

Prohibits a column from being null. Must be declared in line. All other constraints can be declared either inline or out of line.