Populating and Querying tables

Insert, Update, Delete and View (DML)

Inserting data into a table• To add a row of data to a tableINSERT INTO <table> VALUES(value1, value2, …valueN)• If the value list matches the column list

exactly, there is no need to list the column names.

• If the value list does not match the column list exactly, there is a need to list the column names.

Example

• insert into Expert values (2222221,'Dr. O''Meara','Orthopaedic');

• Where the expert table was set up as:-CREATE TABLE Expert (

Expert_Id numeric(7,0),Expert_Name varchar(50),Expertise_area varchar(15),PRIMARY KEY (Expert_Id))

Note also, if you want to put an apostrophe in a string, put in two apostrophes.

Referential integrity

• The above tables have no foreign keys and a straightforward insert does not compromise referential integrity.

• If a table is constrained by foreign key values, then there is a need to see what is in the other table.

• Retrieving data from a database– Data can be retrieved from a table or set of tables

using the SELECT statement

Revisiting Joe’s Yard…

Stock

Stock CodeStock DescriptionUnit Price

* Supplier IdUnitCostPriceStock levelReorder level

Docket

DocketNoOrder Date

* Customer IdDocketPaidSigDocketRcvdSig

* Staff no

Order Line

* DocketNo* Stock CodeQuantityRequired

Customer

Customer IdCustomer NameCustomer Address

Supplier

Supplier IdSupplier NameSupplier AddressAmount Owed

Staff

Staff noStaff nameStaff role

SupplierOrder

SupplierOrderNo* Supplier IdSupplierOrderDateDeliveredDate

SupplierOrderLine

* SupplierOrderNo* Stock CodeStockRequired

Hierarchy of data structure

Stock

Stock CodeStock DescriptionUnit Price

* Supplier IdUnitCostPriceStock levelReorder level

Docket

DocketNoOrder Date

* Customer IdDocketPaidSigDocketRcvdSig

* Staff no

Order Line

* DocketNo* Stock CodeQuantityRequired

Customer

Customer IdCustomer NameCustomer Address

Supplier

Supplier IdSupplier NameSupplier AddressAmount Owed

Staff

Staff noStaff nameStaff role

SupplierOrder

SupplierOrderNo* Supplier IdSupplierOrderDateDeliveredDate

SupplierOrderLine

* SupplierOrderNo* Stock CodeStockRequired

Layers of tables

• The tables Customer, Staff and Supplier have only primary keys. They are the foundation layer. Layer 1.

• The tables Docket, Stock and Supplier Order have foreign keys that only reference the foundation layer. They are Layer 2.

• Order line and Supplier order line depend on the tables in Layer 2. They are layer 3.

Remember the bricks…

Layer 1

Cus

tom

erC

usto

mer

Staf

fSt

aff

Supp

lier

Supp

lier

The customer row is added, with key CustomerId, the Staff with key StaffNo and the Supplier with key SupplierId.

Layer 2

Docket

Stock

Supplier Order

CustomerStaffSupplier

The stock and the supplier Order depend on the Supplier, both having foreign key SupplierId.

The Docket depends on BOTH Staff and Customer, having foreign keys CustomerPdSig, CustomerRcvdSig and CustomerId.

Layer 3

Supplier Staff Customer

DocketStock

Supplier Order

Supplier Supplier Order Order lineline

Order lineOrder line•Both the supplier order line and the order line depend on the stock, having stockcode as a foreign key and part of their key.

•Order line depends on docket.

•Supplier order line depends on Supplier Order

The built database

Recap• Look back at the blocks.

– The table creates are the structure or the framework - i.e. the architect’s drawing

– The inserts are like the bricks. You cannot insert into a table unless there is supporting data in the table on which it depends.

• Do– Creates starting with the one(s) with no dependents– Inserts starting with the one(s) with no dependents– Deletes starting with the one(s) on which no other

depends– Drops starting with the one(s) on which no other depends

Revisiting database structure

ExternalSchema

ConceptualSchema

InternalSchema

PhysicalSchema

The external schema

– Level visible to user– Multiple views of the

system• e.g. View an order -

see limited product and customer information

– Only the database Administrator may access the whole database at this level

• Each external view is defined by means of an external schema– Provides definitions of

each external view.– Written in a Data

Definition Language.– individual to the user or

user group.– accessed through a 3GL,

a query language or a special purpose forms or menu-based language

SQL, DML and DDL

Data manipulation and definition

SQL• Standard Query Language is used widely to

access databases.• Implemented SQL (Oracle, MS SQL Server,

Access) varies a little from the standard, but is reasonably standard

• It consists of a data definition language - DDL (Create, Alter, Drop)

• And a Data Manipulation Language - DML (Select, Union, Update, Delete, Insert Into, Select Into, Transform, Parameter)

DLL - Add a tableCREATE TABLE table_name{(column_name data_type

[NOT NULL] [UNIQUE][DEFAULT default_option][CHECK (search_condition)][,…]}

[PRIMARY KEY (list_of_columns),]{[UNIQUE (list_of_columns),][,…]}{[FOREIGN KEY {(list_of_foreign_key_columns)REFERENCES parent_table_name[(list_of_candidate_key_columns)], [MATCH {PARTIAL | FULL}{[CHECK (search_condition)][,…]})• [] optional, {} one or more, lower case – user supplied

names, upper case reserved words, [|] either or, () are part of the syntax.

Basic create• DDL - Create a tableCreate table Publisher( PubID VARCHAR(10) NOT NULL, PubName VARCHAR(100), PubPhone VARCHAR(20))

Create table Books (ISBN VARCHAR(13) NOT NULL,Title VARCHAR(100),Price Decimal(7,2),PubID VARCHAR(10))

With keysCreate table Publisher (PubID VARCHAR(10) UNIQUE NOT NULL, PubName VARCHAR(100), PubPhone VARCHAR(20),

primary key (PubID))

Create table Books (ISBN VARCHAR(13),Title VARCHAR(100),Price Decimal(7,2),PubID VARCHAR(10),PRIMARY KEY (ISBN),FOREIGN KEY (PubID) REFERENCES PUBLISHER)

DDL - Add a table

• Syntax is as follows:-CREATE TABLE TableName(ColumnDefinition,…[,Multi-ColumnConstraint,…]);

• Column definition isColumnDefinition ::= ColumnName

DataType[(size)][Single-ColumnConstraint]

Constraints

DDL - Single column constraint

• Single-ColumnConstraint:==CONSTRAINTIndexName[PRIMARY KEY | UNIQUE |

REFERENCES ReferencedTable[(ReferencedColumn,…)]

]• The ReferencedColumn is only necessary if the field

being referenced is not the primary key of the referenced table

DDL - Multi-column constraints

• This constraint clause can appear after all column definitions:

CONSTRAINT IndexName [PRIMARY KEY (ColumnName,…) | UNIQUE (ColumnName,…) | FOREIGN KEY (ReferencingColumn,…)

REFERENCES ReferencedTable[(ReferencedColumn,…)] ]

DDL - Create a table

Create table Publisher (PubID TEXT(10) CONSTRAINT PrimaryKeyName PRIMARY KEY, PubName TEXT(100), PubPhone TEXT(20));

Create table Books (ISBN TEXT(13) CONSTRAINT PrimaryKeyName PRIMARY KEY,Title TEXT(100),Price MONEY,PubID TEXT(10) CONSTRAINT FOREIGN KEY PubID REFERENCES

PUBLISHER(PubID));

Constraints on a single column

• [ NULL | NOT NULL ]• { PRIMARY KEY | UNIQUE }• FOREIGN KEY ]

            REFERENCES ref_table [ ( ref_column )– [ ON DELETE { CASCADE | NO ACTION } ] – [ ON UPDATE { CASCADE | NO ACTION } ]

• CHECK ( logical_expression )

Table constraints.• < table_constraint > ::= [ CONSTRAINT constraint_name

] –  { [ { PRIMARY KEY | UNIQUE }

        { ( column [ ASC | DESC ] [ ,...n ] ) }         [ WITH FILLFACTOR = fillfactor ]         [ ON { filegroup | DEFAULT } ]     ]

– FOREIGN KEY         [ ( column [ ,...n ] ) ]         REFERENCES ref_table [ ( ref_column [ ,...n ] ) ]         [ ON DELETE { CASCADE | NO ACTION } ]         [ ON UPDATE { CASCADE | NO ACTION } ]         [ NOT FOR REPLICATION ]     | CHECK [ NOT FOR REPLICATION ]         ( search_conditions )

Widely used constraints

• Primary key• Foreign key• Unique• Check (logical expression)• Not null – do we always want this?

DDL - ALTER or DROP TABLE

• Alter is used to– Add a new column to the table– Delete a column from the table

• Drop is used to delete a table

DDL - Syntax for Alter and Drop

ALTER TABLE TableName ADD ColName ColType[(size)] [unique][not null] |

DROP COLUMN ColName

DROP TABLE TableName

Create examples

• This allows certain constraints to be placed on a column or attribute– E.g. CREATE TABLE CLASS(CLASS_name char(10) CHECK (class_name in

('wmt1','wmt2','wmt3')),class_tutor char(10) unique, not null,max_students integer CHECK max_students

between 1 and 100 default 50,primary key (class_name))

Table Manipulation

• CREATE table …• ALTER table …• DROP table …• These operations work on the TABLE• This is equivalent to a file.

Alter

/* Put in a field that allows the accident to be categorised as

Trivial, Moderate, Serious or Disastrous */

alter table Accidentadd column accident_category char(1) check (accident_category in ('T','M','S','D'));

Row manipulation

• INSERT adds new rows of data to a table.• UPDATE modifies existing data in a table.• DELETE removes rows of data from a

table.

UPDATE

UPDATE <table>SET <expression>WHERE <condition;e.g.UPDATE Northwind.dbo.ProductsSET UnitPrice = UnitPrice * 1.1WHERE CategoryID = 2

DELETE

• DELETE FROM <table>WHERE <searchcondition>

Delete from BusDriver where Staff_No = 5544322;

Exercise• The following tables form part of a database held in a

relational DBMS:– Hotel (Hotel_No, Name, Address)– Room (Room_No, Hotel_No, Type, Price)– Booking (Hotel_No,Guest_No, Date_from, Date_To, Room_No)– Guest (Guest_No, Name, Address)

• where – Hotel contains hotel details and Hotel_No is the primary

key, – Room contains room details for each hotel and (Hotel_No,

Room_No) forms the primary key, – Booking contains details of the bookings and the primary key

comprises (Hotel_No, Guest_No and Date_From)– Guest contains guest details and Guest_No is the primary key.

• Create the database.