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

The ACID PropertiesAND Database Design: Chapter 10

AND Normal Forms AND Chapters 13,14,16

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

Atomicity Use a local log to store a transaction’s

partial result If a transaction does something illegal,

toss out the log

Consistent Check constraints in phase 1

Some are immediate, like domains Others don’t have to be true until the

commit point, like FKs

Isolated Transactions commit in a linear order Serializability is enforced Results become available only after

atomic commit point

Durable Database has one state and it is in

nonvolatile storage Keep checkpoints and transaction logs

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

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

Our focus: normalization Goals

Minimize redundant data Minimize “update anomalies”

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

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.

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.

Example: 1NF

Example: 2NF

Example: 2NF, continued

3NF: remove transitive dependenciesCustomer ID Address ZIP18 112 First 80304 17 123 Ash 80303 16 123 Ash 80303

3NF, continuedBreak into two tables:

Customer ID AddressAddress Zip

4NF: Separate pairs of MVDsMothers_Phone Fathers_Phone Child_Name

Break into: Mothers_Phone Child_Name 3030000000 Sue 3031111111 SueAnd Fathers_Phone Child_Name 3032222222 Sue

3033333333 Sue

Note: both fields needed for PK

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

Autocommit Used when manipulating a MySQL

database interactively Automatically and immediately commits

INSERT UPDATE DELETE commands Use the transaction protocol to override

this

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

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

A Transaction CREATE PROCEDURE test()BEGINDECLARE sql_error TINYINT DEFAULT FALSE;DECLARE CONTINUE HANDLER FOR SQLEXCEPTIONSET sql_error = TRUE;START TRANSACTION; INSERT INTO invoicesVALUES (115, 34, 'ZXA-080', '2012-01-18', 14092.59, 0, 0, 3, '2012-04-18', NULL); INSERT INTO invoice_line_items VALUES (115, 1, 160, 4447.23, 'HW upgrade');

Continued…INSERT INTO invoice_line_items VALUES (115, 2, 167, 9645.36, 'OS upgrade');IF sql_error = FALSE THENCOMMIT;SELECT 'The transaction was committed.';ELSEROLLBACK;SELECT 'The transaction was rolled back.';END IF;END//

SavepointsUSE ap; START TRANSACTION; SAVEPOINT before_invoice;

INSERT INTO invoicesVALUES (115, 34, 'ZXA-080', '2012-01-18', 14092.59, 0, 0, 3, '2012-04-18', NULL); SAVEPOINT before_line_item1; INSERT INTO invoice_line_items VALUES (115, 1, 160, 4447.23, 'HW upgrade'); SAVEPOINT before_line_item2;

Continued…INSERT INTO invoice_line_items VALUES (115, 2, 167, 9645.36,'OS upgrade'); ROLLBACK TO SAVEPOINT before_line_item2;

ROLLBACK TO SAVEPOINT before_line_item1;

ROLLBACK TO SAVEPOINT before_invoice;

COMMIT;

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

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

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

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

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)

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

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

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;

Example, continuedSET 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//

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

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

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;

Example with a cursorDELIMITER // 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;

Example with a CursorIF 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//

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

Syntax of MySQL Triggers:Chapter 16CREATE 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!!

Trigger exampleCREATE 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 vendorsSET vendor_state = 'wi'WHERE vendor_id = 1

** This illustrates a row level trigger

** otherwise, it’s a statement level trigger

Constraint Trigger ExampleCREATE TRIGGER invoices_before_updateBEFORE UPDATE ON invoicesFOR EACH ROWBEGINDECLARE 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

Examples of Audit ConstraintsCREATE TRIGGER invoices_after_insertAFTER INSERT ON invoicesFOR EACH ROWBEGIN INSERT INTO invoices_audit VALUES (NEW.vendor_id, NEW.invoice_number, NEW.invoice_total, 'INSERTED', NOW());END// CREATE TRIGGER invoices_after_deleteAFTER DELETE ON invoicesFOR EACH ROWBEGININSERT INTO invoices_audit VALUES(OLD.vendor_id, OLD.invoice_number,OLD.invoice_total, 'DELETED', NOW());END//

Key Terms! Triggering events (insert, delete,

update) Trigger preconditions (basically a where

clause) Trigger actions (basically a query) Trigger execution (before or after event)