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The ACID Properties AND Database Design: Chapter 10 AND Normal Forms AND Chapters 13,14,16.

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Presentation on theme: "The ACID Properties AND Database Design: Chapter 10 AND Normal Forms AND Chapters 13,14,16."— Presentation transcript:

1 The ACID Properties AND Database Design: Chapter 10 AND Normal Forms AND Chapters 13,14,16

2 ACID Transactions  Atomic: Either all of a transaction or None of it affects the database  Consistent: When a transaction ends, the database obeys all constraints  Isolated: Two running transactions cannot pass values to each other, via the database or other data store  Durable: Once a transaction has “committed”, its updates are permanent

3 Atomicity  Use a local log to store a transaction’s partial result  If a transaction does something illegal, toss out the log

4 Consistent  Check constraints in phase 1  Some are immediate, like domains  Others don’t have to be true until the commit point, like FKs

5 Isolated  Transactions commit in a linear order  Serializability is enforced  Results become available only after atomic commit point

6 Durable  Database has one state and it is in nonvolatile storage  Keep checkpoints and transaction logs

7 Deadlock  Loops of transactions wait on each other  Detection: use time-outs  Prevention: use “waits for” graph

8 The DB Design Process  Start with an entity model  Map to tables  Create PKs and FKs  Create other constraints  Normalize tables

9 Our focus: normalization  Goals  Minimize redundant data  Minimize “update anomalies”

10 Functional and Multivalued Dependencies  FD   We say that ai FD-> aj  Or “ai functionally determines aj”  MVD->  We say that ai MVD-> aj  Or “ai multivalued determines aj”  Note: the right side of an FD or an MVD can be a set of attributes

11 First 3 normal forms  First (1NF)The value stored at the intersection of each row and column must be a scalar value, and a table must not contain any repeating columns.  Second (2NF)Every non-key column must depend on the entire primary key.  Third (3NF)Every non-key column must depend only on the primary key.

12 NF3 fixed and NF4  Boyce-Codd (BCNF)A non-key column can’t be dependent on another non-key column.  Fourth (4NF)A table must not have more than one multivalued dependency, where the primary key has a one-to-many relationship to non-key columns.

13 Example: 1NF

14 Example: 2NF

15 Example: 2NF, continued

16 3NF: remove transitive dependencies Customer ID Address ZIP First Ash Ash 80303

17 3NF, continued Break into two tables: Customer ID Address Address Zip

18 4NF: Separate pairs of MVDs Mothers_Phone Fathers_Phone Child_Name Break into: Mothers_Phone Child_Name Sue Sue And Fathers_Phone Child_Name Sue Sue Note: both fields needed for PK

19 Tradeoffs  “Decomposition” makes it harder to misunderstand the database schema  But Decomposition create narrow tables that might not correspond to forms in the real world  And Decomposition leads to extra joins  One solution is to pre-join data

20 Autocommit  Used when manipulating a MySQL database interactively  Automatically and immediately commits INSERT UPDATE DELETE commands  Use the transaction protocol to override this

21 Chapter 14: Transactions in MySQL  A transaction is the unit of work in a relational database  Not available with the MyISAM engine  InnoDB does support transactions  Storage engines  InnoDB is the default  MyISAM has no foreign keys, but has full text search

22 Transactions  Often used within stored procedures, which are compiled programs that can be called by an application  Operations  START TRANSACTION  COMMIT  ROLLBACK and SAVEPOINT  Used when you don’t want to undo an entire transactions

23 A Transaction CREATE PROCEDURE test() BEGIN DECLARE sql_error TINYINT DEFAULT FALSE; DECLARE CONTINUE HANDLER FOR SQLEXCEPTION SET sql_error = TRUE; START TRANSACTION; INSERT INTO invoices VALUES (115, 34, 'ZXA-080', ' ', , 0, 0, 3, ' ', NULL); INSERT INTO invoice_line_items VALUES (115, 1, 160, , 'HW upgrade');

24 Continued… INSERT INTO invoice_line_items VALUES (115, 2, 167, , 'OS upgrade'); IF sql_error = FALSE THEN COMMIT; SELECT 'The transaction was committed.'; ELSE ROLLBACK; SELECT 'The transaction was rolled back.'; END IF; END//

25 Savepoints USE ap; START TRANSACTION; SAVEPOINT before_invoice; INSERT INTO invoices VALUES (115, 34, 'ZXA-080', ' ', , 0, 0, 3, ' ', NULL); SAVEPOINT before_line_item1; INSERT INTO invoice_line_items VALUES (115, 1, 160, , 'HW upgrade'); SAVEPOINT before_line_item2;

26 Continued… INSERT INTO invoice_line_items VALUES (115, 2, 167, ,'OS upgrade'); ROLLBACK TO SAVEPOINT before_line_item2; ROLLBACK TO SAVEPOINT before_line_item1; ROLLBACK TO SAVEPOINT before_invoice; COMMIT;

27 Another view of transactions  Prevents  Lost updates from one of two transactions  Dirty reads when a transaction reads an uncommitted value  Nonrepeatable reads in one transaction because the value gets updated in between  Phantom reads are when a selection query is run twice in a transaction and returns different results

28 Transaction Isolation Leves  Set transaction level  Next (no keyword) sets the transaction in the current session  Session sets all transactions in a session  Global sets all transactions for all sessions

29 Continued…  Options  Serializable isolates transactions completely and is the highest level of protection  Read uncommitted lets our four problems occur – no locks  Read committed prevents dirty reads but allows the other problems by not allowing uncommitted writes from being read  Repeatable read is the default and it means that a transaction will always read a given value the same because the values are locked

30 Deadlock  Detect by closing transactions that have been open a long time  Use the lowest acceptable locking level  Try to do heavy update transactions when database can be completely reserved

31 Stored programs  Stored procedures (can be called by an application)  Stored functions (can be called by an SQL program)  Triggers (tied to an operation like INSERT)  Events (tied to a clock)

32 Flow of control in SQL  IF - ELSE  CASE – WHEN - ELSE  WHILE – DO - LOOP  REPEAT - UNTIL – END REPEAT

33 Variables  DECLARE statement  SET statement  DEFAULT statement  INTO (from a SELECT clause)

34 Example (stored procedure)… CREATE PROCEDURE test() BEGIN DECLARE max_invoice_total DECIMAL(9,2); DECLARE min_invoice_total DECIMAL(9,2); DECLARE percent_difference DECIMAL(9,4); DECLARE count_invoice_id INT; DECLARE vendor_id_var INT; SET vendor_id_var = 95; SELECT MAX(invoice_total), MIN(invoice_total), COUNT(invoice_id) INTO max_invoice_total, min_invoice_total, count_invoice_id FROM invoices WHERE vendor_id = vendor_id_var;

35 Example, continued SET percent_difference = (max_invoice_total - min_invoice_total) / min_invoice_total * 100; SELECT CONCAT('$', max_invoice_total) AS 'Maximum invoice', CONCAT('$', min_invoice_total) AS 'Minimum invoice', CONCAT('%', ROUND(percent_difference, 2)) AS 'Percent difference', count_invoice_id AS 'Number of invoices'; END//

36 Domain types – chapter 8  Character  Integers  Reals  Date  Time  Large object, BLOB and CLOB  2D vector spatial types  Enumerated

37 Conversion  Automatic (implied)  CAST is the standardized operator  CONVERT is similar

38 Cursor syntax  Declare a cursor  DECLARE cursor_name CURSOR FOR select_statement;  Declare an error handler for when no rows are found in the cursor  DECLARE CONTINUE HANDLER FOR NOT FOUND handler_statement;  Open the cursor  OPEN cursor_name;  Get column values from the row and store them in a series of variables  FETCH cursor_name INTO variable1  [, variable2][, variable3]...;  Close the cursor  CLOSE cursor_name;

39 Example with a cursor DELIMITER // CREATE PROCEDURE test() BEGIN DECLARE invoice_id_var INT; DECLARE invoice_total_var DECIMAL(9,2); DECLARE row_not_found TINYINT DEFAULT FALSE; DECLARE update_count INT DEFAULT 0; DECLARE invoices_cursor CURSOR FOR SELECT invoice_id, invoice_total FROM invoices WHERE invoice_total - payment_total - credit_total > 0; DECLARE CONTINUE HANDLER FOR NOT FOUND SET row_not_found = TRUE; OPEN invoices_cursor; WHILE row_not_found = FALSE DO FETCH invoices_cursor INTO invoice_id_var, invoice_total_var;

40 Example with a Cursor IF invoice_total_var > 1000 THEN UPDATE invoices SET credit_total = credit_total + (invoice_total *.1) WHERE invoice_id = invoice_id_var; SET update_count = update_count + 1; END IF; END WHILE; CLOSE invoices_cursor; SELECT CONCAT(update_count, ' row(s) updated.'); END//

41 Triggers  ON event IF precondition THEN action  All three actions could be SQL  Precondition would be a yes/no, based on results  When are they used?  DELETE, UPDATE, INSERT statements

42 Syntax of MySQL Triggers: Chapter 16 CREATE TRIGGER trigger_name {BEFORE|AFTER} {INSERT|UPDATE|DELETE} ON table_name FOR EACH ROW !! Notice that we can look over the threshold of a state change!!

43 Trigger example CREATE TRIGGER vendors_before_update BEFORE UPDATE ON vendors FOR EACH ROW BEGIN SET NEW.vendor_state = UPPER(NEW.vendor_state); END// ** this puts the field in upper case UPDATE vendors SET vendor_state = 'wi' WHERE vendor_id = 1 ** This illustrates a row level trigger ** otherwise, it’s a statement level trigger

44 Constraint Trigger Example CREATE TRIGGER invoices_before_update BEFORE UPDATE ON invoices FOR EACH ROW BEGIN DECLARE sum_line_item_amount DECIMAL(9,2); SELECT SUM(line_item_amount) INTO sum_line_item_amount FROM invoice_line_items WHERE invoice_id = NEW.invoice_id; IF sum_line_item_amount != NEW.invoice_total THEN SIGNAL SQLSTATE 'HY000' SET MESSAGE_TEXT = 'Line item total must match invoice total.'; END IF; END

45 Examples of Audit Constraints CREATE TRIGGER invoices_after_insert AFTER INSERT ON invoices FOR EACH ROW BEGIN INSERT INTO invoices_audit VALUES (NEW.vendor_id, NEW.invoice_number, NEW.invoice_total, 'INSERTED', NOW()); END// CREATE TRIGGER invoices_after_delete AFTER DELETE ON invoices FOR EACH ROW BEGIN INSERT INTO invoices_audit VALUES (OLD.vendor_id, OLD.invoice_number, OLD.invoice_total, 'DELETED', NOW()); END//

46 Key Terms!  Triggering events (insert, delete, update)  Trigger preconditions (basically a where clause)  Trigger actions (basically a query)  Trigger execution (before or after event)


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