1. Sequences Sequences: a database object that generates unique numbers from an arithmetic series. Used to populated surrogate keys. Syntax: CREATE SEQUENCE [INCREMENT BY ] [START WITH ], [MAXVALUE ] [NOMAXVALUE] [CACHE ] [NOCACHE]; Using sequences generate new sequence values: sequence_name.nextval access the current sequence value: sequence_name.currval undefined until the first sequence value is generated SQL> create sequence vendor_seq start with 1 increment by 1; Sequence created. SQL> select vendor_seq.nextval from dual; NEXTVAL --------- 1 SQL> select vendor_seq.currval from dual; CURRVAL --------- 1

2. Creating custom forms Adding more interface items and making it more user-friendly Step0: Connect with the database server Step1: Create a non-database block manually (not using the wizard) Step2: Create a canvas from object navigator Step3: Go to the layout editor Step4: Add interface items (buttons, text items, radio buttons, etc.) Step5: Change the properties of the interface items from property pallette Creating radio buttons: Step1: Go to the layout editor Step2: Select the radio button icon from the left hand margin and place it on the canvas Step3: From the property palette, change the name, label, and value Step4: From the object navigator, select the radio group Step5: Change the name, and set a initial value for the radio group Creating control buttons (refer to page 190 in book) Create buttons Change labels Change hints (see help property group in property palette Create WHEN-BUTTON-PRESSED triggers

3. Layout editor Radio button Text item Display item

5. Trigger codes CREATE_BUTTON (refer to page 193): --clear the form CLEAR_FORM; --assign form state to insert :GLOBAL.mode := 'INSERT'; select itemid_seq.nextval into :item_control_block.itemid_text from dual; Explanation: Global variables are used for form characteristics Purpose: clear any information in the form use the sequence itemid_seq (created previously) to generate a new item id :GLOBAL.mode: the form can be in various modes enter_query, execute_query, insert, update :item_control_block.itemid_text: an item is referred to as :block-name.item-name dual: a dummy table used to complete SQL syntax

6. Trigger code SAVE_BUTTON (refer to page 198) if :global.mode = 'INSERT' then insert into item values (:item_control_block.itemid_text, :item_control_block.itemdesc_text, :item_control_block.category_radio_group); :global.mode := 'UPDATE'; elsif :global.mode = 'UPDATE' then update item set itemdesc = :item_control_block.itemdesc_text, category = :item_control_block.category_radio_group where itemid = :item_control_block.itemid_text; end if; commit; --clear_form; The last command (clear_form) is commented so that you can see the record after it is saved --delete the current record delete from ITEM where itemid = :item_control_block.itemid_text; --commit the changes commit; --clear the form clear_form; DELETE_BUTTON (see page 209)

7. Testing the form Ids (itemID, LOCID, etc.) should be display items. Right now, the form is not ready for querying You can only create a new record, and update a record that you just created Once you create a record and save it, go to SQL*Plus editor and check if the record has been posted in the database If you get the error message: FRM:40735: WHEN-BUTTON-PRESSED trigger raised unhandled exception ORA-01407 it means that you are trying to enter a null value to a non-null field Ignore the message: FRM: 40401: No changes to save, but check if the changes have been made from the SQL*Plus editor. Format mask (refer to page 236) Purpose: to display data in certain formats item property set from property palette