05 ICT118 SQL Constraints Sem 2 2010

8/2/2019 05 ICT118 SQL Constraints Sem 2 2010

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Database and InformationDatabase and InformationDatabase and InformationDatabase and Information

RetrievalRetrievalRetrievalRetrieval

ICT118

Lecture 5 Implementing business rules throughdatabase constraints

22 July, 2010 ICT118 Database and Information Retrieval, Sem 2, 2010 5.2

Oracle 11g: SQL

Chapter 4

ConstraintsSlides from the Cengage website for Casteel, “Oracle 11g: SQL”


ObjectivesObjectivesObjectivesObjectives

Explain the purpose of constraints in a tableExplain the purpose of constraints in a tableExplain the purpose of constraints in a tableExplain the purpose of constraints in a table

Distinguish among PRIMARY KEY, FOREIGN KEY,Distinguish among PRIMARY KEY, FOREIGN KEY,Distinguish among PRIMARY KEY, FOREIGN KEY,Distinguish among PRIMARY KEY, FOREIGN KEY,UNIQUE, CHECK, and NOT NULL constraintsUNIQUE, CHECK, and NOT NULL constraintsUNIQUE, CHECK, and NOT NULL constraintsUNIQUE, CHECK, and NOT NULL constraintsand the appropriate use for each constraint and the appropriate use for each constraint and the appropriate use for each constraint and the appropriate use for each constraint

Understand how constraints can be created whenUnderstand how constraints can be created whenUnderstand how constraints can be created whenUnderstand how constraints can be created whencreating a table or modifying an existing tablecreating a table or modifying an existing tablecreating a table or modifying an existing tablecreating a table or modifying an existing table

Distinguish between creating constraints at theDistinguish between creating constraints at theDistinguish between creating constraints at theDistinguish between creating constraints at thecolumn level and table levelcolumn level and table levelcolumn level and table levelcolumn level and table level



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Objectives (continued)Objectives (continued)Objectives (continued)Objectives (continued)

Create PRIMARY KEY constraints for a singleCreate PRIMARY KEY constraints for a singleCreate PRIMARY KEY constraints for a singleCreate PRIMARY KEY constraints for a single

column and a composite primary keycolumn and a composite primary keycolumn and a composite primary keycolumn and a composite primary key

Create a FOREIGN KEY constraint Create a FOREIGN KEY constraint Create a FOREIGN KEY constraint Create a FOREIGN KEY constraint

Create a UNIQUE constraint Create a UNIQUE constraint Create a UNIQUE constraint Create a UNIQUE constraint

Create a CHECK constraint Create a CHECK constraint Create a CHECK constraint Create a CHECK constraint


Objectives (continued)Objectives (continued)Objectives (continued)Objectives (continued)

Create a NOT NULL constraint using theCreate a NOT NULL constraint using theCreate a NOT NULL constraint using theCreate a NOT NULL constraint using the

ALTER TABLE…MODIFY commandALTER TABLE…MODIFY commandALTER TABLE…MODIFY commandALTER TABLE…MODIFY command

Include constraints during table creationInclude constraints during table creationInclude constraints during table creationInclude constraints during table creation

Use DISABLE and ENABLE commandsUse DISABLE and ENABLE commandsUse DISABLE and ENABLE commandsUse DISABLE and ENABLE commands

Use the DROP commandUse the DROP commandUse the DROP commandUse the DROP command


ConstraintsConstraintsConstraintsConstraints

Rules used to enforce business rules,Rules used to enforce business rules,Rules used to enforce business rules,Rules used to enforce business rules,

practices, and policiespractices, and policiespractices, and policiespractices, and policies

Rules used to ensure accuracy and integrity of Rules used to ensure accuracy and integrity of Rules used to ensure accuracy and integrity of Rules used to ensure accuracy and integrity of

datadatadatadata



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Constraint TypesConstraint TypesConstraint TypesConstraint Types


Creating ConstraintsCreating ConstraintsCreating ConstraintsCreating Constraints

Use the optional CONSTRAINT keyword duringUse the optional CONSTRAINT keyword duringUse the optional CONSTRAINT keyword duringUse the optional CONSTRAINT keyword during

creation to assign a namecreation to assign a namecreation to assign a namecreation to assign a name

Let the server name the constraint using theLet the server name the constraint using theLet the server name the constraint using theLet the server name the constraint using the

default format SYS_Cdefault format SYS_Cdefault format SYS_Cdefault format SYS_Cn nn n

Informative names can assist in debuggingInformative names can assist in debuggingInformative names can assist in debuggingInformative names can assist in debugging


Creating ConstraintsCreating ConstraintsCreating ConstraintsCreating Constraints(continued)(continued)(continued)(continued)WhenWhenWhenWhen

During table creation

After table creation, by modifying the existing table

HowHowHowHow

Column level approach

Table level approach



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Creating Constraints at theCreating Constraints at theCreating Constraints at theCreating Constraints at the

Column LevelColumn LevelColumn LevelColumn Level

If a constraint is being created at the columnIf a constraint is being created at the columnIf a constraint is being created at the columnIf a constraint is being created at the column

level, the constraint applies to the columnlevel, the constraint applies to the columnlevel, the constraint applies to the columnlevel, the constraint applies to the column

specifiedspecifiedspecifiedspecified


Creating Constraints at the TableCreating Constraints at the TableCreating Constraints at the TableCreating Constraints at the Table

LevelLevelLevelLevel

Approach can be used to create anyApproach can be used to create anyApproach can be used to create anyApproach can be used to create anyconstraint type except NOT NULLconstraint type except NOT NULLconstraint type except NOT NULLconstraint type except NOT NULL

Required if constraint is based on multipleRequired if constraint is based on multipleRequired if constraint is based on multipleRequired if constraint is based on multiplecolumnscolumnscolumnscolumns


Enforcement of ConstraintsEnforcement of ConstraintsEnforcement of ConstraintsEnforcement of Constraints

All constraints are enforced at the table levelAll constraints are enforced at the table levelAll constraints are enforced at the table levelAll constraints are enforced at the table level

If a data value violates a constraint, the entireIf a data value violates a constraint, the entireIf a data value violates a constraint, the entireIf a data value violates a constraint, the entire

row is rejectedrow is rejectedrow is rejectedrow is rejected



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Adding Constraints to ExistingAdding Constraints to ExistingAdding Constraints to ExistingAdding Constraints to Existing

TablesTablesTablesTablesConstraints are added to an existing table withConstraints are added to an existing table withConstraints are added to an existing table withConstraints are added to an existing table with

the ALTER TABLE commandthe ALTER TABLE commandthe ALTER TABLE commandthe ALTER TABLE command

Add a NOT NULL constraint using MODIFYAdd a NOT NULL constraint using MODIFYAdd a NOT NULL constraint using MODIFYAdd a NOT NULL constraint using MODIFY

clauseclauseclauseclause

All other constraints are added using ADDAll other constraints are added using ADDAll other constraints are added using ADDAll other constraints are added using ADD

clauseclauseclauseclause


Using the PRIMARY KEYUsing the PRIMARY KEYUsing the PRIMARY KEYUsing the PRIMARY KEY

Constraint Constraint Constraint Constraint

Ensures that columns do not containEnsures that columns do not containEnsures that columns do not containEnsures that columns do not contain

duplicate or NULL valuesduplicate or NULL valuesduplicate or NULL valuesduplicate or NULL values

Only one per table is allowedOnly one per table is allowedOnly one per table is allowedOnly one per table is allowed


Constraint Checked withConstraint Checked withConstraint Checked withConstraint Checked withData Input Data Input Data Input Data Input



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PRIMARY KEY Constraint forPRIMARY KEY Constraint forPRIMARY KEY Constraint forPRIMARY KEY Constraint for

Composite KeyComposite KeyComposite KeyComposite KeyList column names within parenthesesList column names within parenthesesList column names within parenthesesList column names within parentheses

separated by commasseparated by commasseparated by commasseparated by commas


Using the FOREIGN KEYUsing the FOREIGN KEYUsing the FOREIGN KEYUsing the FOREIGN KEY

Constraint Constraint Constraint Constraint

Requires a value to exist in the referencedRequires a value to exist in the referencedRequires a value to exist in the referencedRequires a value to exist in the referenced

column of another tablecolumn of another tablecolumn of another tablecolumn of another table

NULL values are allowedNULL values are allowedNULL values are allowedNULL values are allowed

Enforces referential integrityEnforces referential integrityEnforces referential integrityEnforces referential integrity

Maps to the PRIMARY KEY in parent tableMaps to the PRIMARY KEY in parent tableMaps to the PRIMARY KEY in parent tableMaps to the PRIMARY KEY in parent table


FOREIGN KEY Constraint FOREIGN KEY Constraint FOREIGN KEY Constraint FOREIGN KEY Constraint ExampleExampleExampleExample



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Deletion of Foreign Key ValuesDeletion of Foreign Key ValuesDeletion of Foreign Key ValuesDeletion of Foreign Key Values

YouYouYouYou cannot cannot cannot cannot delete a value in a parent tabledelete a value in a parent tabledelete a value in a parent tabledelete a value in a parent table

referenced by a row in a child tablereferenced by a row in a child tablereferenced by a row in a child tablereferenced by a row in a child table

Use ON DELETE CASCADE keywords whenUse ON DELETE CASCADE keywords whenUse ON DELETE CASCADE keywords whenUse ON DELETE CASCADE keywords when

creating FOREIGN KEY constraint creating FOREIGN KEY constraint creating FOREIGN KEY constraint creating FOREIGN KEY constraint – –– – thisthisthisthis

clause automatically deletes a parent rowclause automatically deletes a parent rowclause automatically deletes a parent rowclause automatically deletes a parent row

when the row in a child table is deletedwhen the row in a child table is deletedwhen the row in a child table is deletedwhen the row in a child table is deleted


Using the UNIQUE Constraint Using the UNIQUE Constraint Using the UNIQUE Constraint Using the UNIQUE Constraint

No duplicates are allowed in the referencedNo duplicates are allowed in the referencedNo duplicates are allowed in the referencedNo duplicates are allowed in the referenced

columncolumncolumncolumn

NULL values are permittedNULL values are permittedNULL values are permittedNULL values are permitted


Using the CHECK Constraint Using the CHECK Constraint Using the CHECK Constraint Using the CHECK Constraint

Updates and additions must meet Updates and additions must meet Updates and additions must meet Updates and additions must meet

specified conditionspecified conditionspecified conditionspecified condition



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Using the NOT NULL Constraint Using the NOT NULL Constraint Using the NOT NULL Constraint Using the NOT NULL Constraint

The NOT NULL constraint is a special CHECKThe NOT NULL constraint is a special CHECKThe NOT NULL constraint is a special CHECKThe NOT NULL constraint is a special CHECK

constraint with IS NOT NULL conditionconstraint with IS NOT NULL conditionconstraint with IS NOT NULL conditionconstraint with IS NOT NULL condition

Can only be created at column levelCan only be created at column levelCan only be created at column levelCan only be created at column level

Included in output of DESCRIBE commandIncluded in output of DESCRIBE commandIncluded in output of DESCRIBE commandIncluded in output of DESCRIBE command

Can only be added to an existing table usingCan only be added to an existing table usingCan only be added to an existing table usingCan only be added to an existing table using

ALTER TABLE…MODIFY commandALTER TABLE…MODIFY commandALTER TABLE…MODIFY commandALTER TABLE…MODIFY command


NOT NULL Constraint ExampleNOT NULL Constraint ExampleNOT NULL Constraint ExampleNOT NULL Constraint Example


Including Constraints duringIncluding Constraints duringIncluding Constraints duringIncluding Constraints during

Table CreationTable CreationTable CreationTable Creation – –– – Column LevelColumn LevelColumn LevelColumn Level

Include in column definitionInclude in column definitionInclude in column definitionInclude in column definition



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Including Constraints duringIncluding Constraints duringIncluding Constraints duringIncluding Constraints during

Table CreationTable CreationTable CreationTable Creation – –– – Table LevelTable LevelTable LevelTable LevelInclude at end of column list Include at end of column list Include at end of column list Include at end of column list


Multiple Constraints on aMultiple Constraints on aMultiple Constraints on aMultiple Constraints on a

Single ColumnSingle ColumnSingle ColumnSingle ColumnA column may be included in multipleA column may be included in multipleA column may be included in multipleA column may be included in multiple

constraintsconstraintsconstraintsconstraints

The order# column is included in a primary keyThe order# column is included in a primary keyThe order# column is included in a primary keyThe order# column is included in a primary key

and a foreign key constraint and a foreign key constraint and a foreign key constraint and a foreign key constraint


Viewing ConstraintsViewing ConstraintsViewing ConstraintsViewing Constraints – –– – USER_CONSTRAINTSUSER_CONSTRAINTSUSER_CONSTRAINTSUSER_CONSTRAINTS

Display constraint listing for a specificDisplay constraint listing for a specificDisplay constraint listing for a specificDisplay constraint listing for a specific

tabletabletabletable



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Viewing ConstraintsViewing ConstraintsViewing ConstraintsViewing Constraints – –– –

USER_CONS_COLUMNSUSER_CONS_COLUMNSUSER_CONS_COLUMNSUSER_CONS_COLUMNS

Display constraint listing by columnDisplay constraint listing by columnDisplay constraint listing by columnDisplay constraint listing by column


Using DISABLE/ENABLEUsing DISABLE/ENABLEUsing DISABLE/ENABLEUsing DISABLE/ENABLE

Use DISABLE or ENABLE clause of ALTERUse DISABLE or ENABLE clause of ALTERUse DISABLE or ENABLE clause of ALTERUse DISABLE or ENABLE clause of ALTER

TABLE commandTABLE commandTABLE commandTABLE command


Dropping ConstraintsDropping ConstraintsDropping ConstraintsDropping Constraints

Constraints cannot be modified; they must beConstraints cannot be modified; they must beConstraints cannot be modified; they must beConstraints cannot be modified; they must be

dropped and redropped and redropped and redropped and re----createdcreatedcreatedcreated

Actual syntax depends on the type of Actual syntax depends on the type of Actual syntax depends on the type of Actual syntax depends on the type of

constraint constraint constraint constraint

PRIMARY KEY – just list type of constraint

UNIQUE – include column name

All others – reference the constraint name



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ALTER TABLE…DROP SyntaxALTER TABLE…DROP SyntaxALTER TABLE…DROP SyntaxALTER TABLE…DROP Syntax


Drop Constraint ExampleDrop Constraint ExampleDrop Constraint ExampleDrop Constraint Example


Drop Constraint ExampleDrop Constraint ExampleDrop Constraint ExampleDrop Constraint Example – –– – ErrorErrorErrorError



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SummarySummarySummarySummary

A constraint is a rule that is applied to dataA constraint is a rule that is applied to dataA constraint is a rule that is applied to dataA constraint is a rule that is applied to data

being added to a tablebeing added to a tablebeing added to a tablebeing added to a tableThe constraint represents business rules, policies,

and/or procedures

Data violating the constraint is not added to the

table

A constraint can be included during tableA constraint can be included during tableA constraint can be included during tableA constraint can be included during table

creation as part of the CREATE TABLEcreation as part of the CREATE TABLEcreation as part of the CREATE TABLEcreation as part of the CREATE TABLEcommand or added to an existing tablecommand or added to an existing tablecommand or added to an existing tablecommand or added to an existing table

using the ALTER TABLE commandusing the ALTER TABLE commandusing the ALTER TABLE commandusing the ALTER TABLE command


Summary (continued)Summary (continued)Summary (continued)Summary (continued)

A PRIMARY KEY constraint does not allow duplicate orA PRIMARY KEY constraint does not allow duplicate orA PRIMARY KEY constraint does not allow duplicate orA PRIMARY KEY constraint does not allow duplicate or

NULL values in the designated columnNULL values in the designated columnNULL values in the designated columnNULL values in the designated column

Only one PRIMARY KEY constraint is allowed in a tableOnly one PRIMARY KEY constraint is allowed in a tableOnly one PRIMARY KEY constraint is allowed in a tableOnly one PRIMARY KEY constraint is allowed in a table

A FOREIGN KEY constraint requires that the column entryA FOREIGN KEY constraint requires that the column entryA FOREIGN KEY constraint requires that the column entryA FOREIGN KEY constraint requires that the column entry

match a referenced column entry in the referenced tablematch a referenced column entry in the referenced tablematch a referenced column entry in the referenced tablematch a referenced column entry in the referenced table

or be NULLor be NULLor be NULLor be NULL

A UNIQUE constraint is similar to a PRIMARY KEYA UNIQUE constraint is similar to a PRIMARY KEYA UNIQUE constraint is similar to a PRIMARY KEYA UNIQUE constraint is similar to a PRIMARY KEYconstraint except it allows NULL values to be stored inconstraint except it allows NULL values to be stored inconstraint except it allows NULL values to be stored inconstraint except it allows NULL values to be stored inthe specified columnthe specified columnthe specified columnthe specified column

A CHECK constraint ensures a value meets a specifiedA CHECK constraint ensures a value meets a specifiedA CHECK constraint ensures a value meets a specifiedA CHECK constraint ensures a value meets a specifiedconditionconditionconditioncondition


Summary (continued)Summary (continued)Summary (continued)Summary (continued)

A NOT NULL constraint ensures a value isA NOT NULL constraint ensures a value isA NOT NULL constraint ensures a value isA NOT NULL constraint ensures a value isalways provided for a columnalways provided for a columnalways provided for a columnalways provided for a column

A constraint can be disabled or enabled usingA constraint can be disabled or enabled usingA constraint can be disabled or enabled usingA constraint can be disabled or enabled usingthe ALTER TABLE command and the DISABLEthe ALTER TABLE command and the DISABLEthe ALTER TABLE command and the DISABLEthe ALTER TABLE command and the DISABLEand ENABLE keywordsand ENABLE keywordsand ENABLE keywordsand ENABLE keywords

A constraint cannot be modifiedA constraint cannot be modifiedA constraint cannot be modifiedA constraint cannot be modifiedTo change a constraint, the constraint must first bedropped with the DROP command and then re-created

USER_CONSTRAINTS andUSER_CONSTRAINTS andUSER_CONSTRAINTS andUSER_CONSTRAINTS andUSER_CONS_COLUMNS data dictionary viewsUSER_CONS_COLUMNS data dictionary viewsUSER_CONS_COLUMNS data dictionary viewsUSER_CONS_COLUMNS data dictionary viewsprovide information regarding constraintsprovide information regarding constraintsprovide information regarding constraintsprovide information regarding constraints

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05 ICT118 SQL Constraints Sem 2 2010