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Sequences

Sequences. Sequences: a database object that generates unique numbers from an arithmetic series. Used to populated surrogate keys. Syntax: CREATE SEQUENCE <sequence_name> [INCREMENT BY <interval>] [START WITH <value>],

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Sequences

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  1. Sequences • Sequences: a database object that generates unique numbers from an arithmetic • series. Used to populated surrogate keys. • Syntax: CREATE SEQUENCE <sequence_name> • [INCREMENT BY <interval>] [START WITH <value>], • [MAXVALUE <maximum value>] [NOMAXVALUE] • [CACHE <# of values to cache>] [NOCACHE]; SQL> create sequence vendor_seq start with 1 increment by 1; Sequence created. • 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> 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

  4. 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

  5. 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_BUTTON (see page 209) --delete the current record delete from ITEM where itemid = :item_control_block.itemid_text; --commit the changes commit; --clear the form clear_form;

  6. Format mask (refer to page 236) • Purpose: to display data in certain formats • item property set from property palette 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.

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