Note that:A unique or primary key constraint can use either a unique index, an entire nonunique index, or the first few columns of a nonunique index.If a unique or primary key constraint uses a nonunique index, then no other unique or primary key constraint can use that nonunique index.The column order in the constraint and index need not match.The object number of the index used by a unique or primary key constraint is stored in If an enabled unique or primary key constraint is using an index, you cannot drop only the index. To designate a primary key, use the Whenever practical, choose as the primary key a single column whose values are generated by a sequence.The second-best choice for a primary key is a single column whose values are all of the following:Minimize your use of composite primary keys, whose values are long and cannot be generated by a sequence.Customer phone number (country code column, area code column, and local phone number column)Figure 12-1 Rows That Violate and Satisfy a UNIQUE ConstraintWhen two tables share one or more columns, you use can use a Figure 12-2 Rows That Violate and Satisfy a FOREIGN KEY ConstraintIn general, it is not possible to use declarative referential integrity to enforce the Several relationships between parent and child tables can be determined by the other types of constraints defined on the foreign key in the child table.When no other constraints are defined on the foreign key, any number of rows in the child table can reference the same parent key value. You don't do it, how could it enforce integrity when the data is private to your session? presented here should apply to most relational database systems, your SQL write a SQL script that performs these tasks in the following order: Following this order avoids most chicken-and-egg problems that may occur entity-relationship (E-R) diagram for this database. using Oracle. In relationships, data is linked between two or more tables.This is achieved by having the foreign key (in the associated table) reference a primary key value (in the primary – or parent – table). For example:When loading large amounts of data into a table using SQL*LoaderWhen performing batch operations that make massive changes to a table (such as changing each employee number by adding 1000 to the existing number)Temporarily turning off constraints can speed up these operations.When you define an integrity constraint (using either You define and disable an integrity constraint (using either After you have cleansed the data and filled the empty columns, you can enable constraints that were disabled during data insertion.If you must perform a large insert or update when a table contains data, you can temporarily disable constraints to improve performance of the bulk operation.If a row of a table disobeys an integrity constraint, then this row is in violation of the constraint and is called an You can identify exceptions for a specific integrity constraint as you try to enable the constraint.When you try to create or enable a constraint, and the statement fails because integrity constraint exceptions exist, the statement is rolled back. key in the This is all you need to know to use primary and foreign keys in Oracle. If you expand the previous example by adding a Oracle Database allows a column to be referenced by multiple When Oracle Database checks a constraint, it signals an error if the constraint is not satisfied.
For a developer to identify and disable … Re: Enable/Disable referential integrity Mohamid May 29, 2011 8:56 PM ( in response to sybrand_b ) Because i am exporting tables which has got some columns which refers to the another table data .And to prevent inconsistency i need to disable all the constraints . in another application such as Microsoft Word. only way to preserve the diagram is to copy-and-paste an image of it into Fortunately, Oracle has the power to enforce referential integrity, but to do so, we must inform the database of the relationships involved.