Working with Derby

RHS – 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 – Creating tables Before using a database, we must connect to it Right-click on database, and choose ”Connect”

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

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

RHS – Creating tables Right-click on ”Tables”, and choose ”Create table”

RHS – Creating tables

RHS – 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

RHS – Creating tables Enter a proper name for the table

RHS – 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

RHS – 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…?)

RHS – 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)

RHS – Creating tables

RHS – Creating tables A database called Phone Book A table called Friend Two data fields: Name, Phone Red indicates that field is part of key field

RHS – Creating tables We can add more data fields later Right-click on the table, choose ”Add Column…”

RHS – Creating tables Same as before, but different dialog…

RHS – 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 ClubMember LastSale Sale CustomerNumber ItemNumber Date NumberOfItems TotalAmount SentToCustomer PaymentReceived

RHS – 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…”

RHS – Adding data Data in the table is shown here (none yet….)

RHS – Adding data Press this icon to add new data

RHS – Adding data Type in data for this particular record

RHS – Adding data

RHS – Adding data Table now con- tains one record

RHS – Adding data And so on, and so on…

RHS – 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…

RHS – Adding data What is wrong here…?

RHS – Adding data

RHS – 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 ( )

RHS – Adding data What is this…? An SQL query!

RHS – 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