Working with Derby

RHS – 2009 2

Creating tables

• We know how to create a database in Derby – an empty database

• Next step is to add tables to the database

• After adding tables, we can enter data into the tables

• Remember; design your tables BEFORE using Derby to enter them

RHS – 2009 3

Creating tables

Before using a database, we must connect to it

Right-click on database, and choose ”Connect”

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Creating tables

Enter whatever we chose when crea-ting the database(hopefully just blanks…)

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Creating tables

Now we can access the tables in the database – but there are none yet

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Creating tables

Right-click on ”Tables”, and choose ”Create table”

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Creating tables

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Creating tables

• Recall what we need in order to define a table– A proper name for the table– A set of field definitions – a name and a type

for each field– A key field – one or more fields the

combination of which is always unique

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Creating tables

Enter a proper name for the table

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Creating tables• For each data field (also called column),

we must add quite a lot of information:– Column name: Name of the data field– Key: Is the field part of the key field– Index: Leave as-is…– Null: Can we omit the value– Unique: Must the value be unique– Data type: Proper type of data– Size: How large can the data be

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Creating tables• Example: a Name field

– Column name: Name– Key: Yes– Null: No– Unique: (decided by choosing ”Key”)– Data type: VARCHAR (means ”String”)– Size: 50 (how long can a name be…?)

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Creating tables• Example: a Phone field

– Column name: Phone– Key: Yes– Null: No– Unique: (decided by choosing ”Key”)– Data type: NUMERIC (number)– Size: 8 (a Danish phone number)

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Creating tables

RHS – 2009 14

Creating tables

A database called Phone Book

A table called Friend

Two data fields: Name, PhoneRed indicates

that field is part of key field

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Creating tables

We can add more data fields later

Right-click on the table, choose ”Add Column…”

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Creating tables

Same as before, but different dialog…

RHS – 2009 17

Creating tables

Exercise– Create a database called WebShop in Derby– Create three tables in WebShop, called Item, Customer, Sale– Definitions of the tables are given below (key fields are in red)

Item ItemNumber ItemName Price Weight NumberInStock IsFragile Description

Customer CustomerNumber Name Address ZipCode E-mail ClubMember LastSale

Sale CustomerNumber ItemNumber Date NumberOfItems TotalAmount SentToCustomer PaymentReceived

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Adding data

With the table defini-tion in place, we can now begin to add data to the table

Right-click on the table, choose ”View Data…”

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Adding data

Data in the table is shown here (none yet….)

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Adding data

Press this icon to add new data

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Adding data

Type in data for this particular record

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Adding data

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Adding data

Table now con-tains one record

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Adding data

And so on, and so on…

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Adding data

• What can go wrong…?

• We might try to type in some data, that does not match the type specification for a particular field

• Derby will complain…

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Adding data

What is wrong here…?

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Adding data

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Adding data

• The error messages can be more or less easy to understand…

• It is almost always a matter of trying to enter data of the wrong type

• Might also be data of incorrect size

• Some errors are more subtle, like a wrong date (30-02-1988)

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Adding data

What is this…?An SQL query!

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Adding data

Exercise– Add a few records to the tables created in the earlier exercise.

Try to experiment with the data, such that you also try to add some data with errors. Observe the errors messages that Derby returns when data has errors

– Do you now feel comfortable working with Derby, with regards to creating databases, tables and fields, and entering data into tables? If not, then try to invent some more tables, enter them into a database, and enter some data into the tables