SQL ACTION QUERIES AND TRANSACTION CONTROLCS 260

Database Systems

Overview

Inserting data Updating/deleting data Surrogate keys Transaction control

Inserting Data

SQL INSERT statements Used to insert new data into a database

table Used when migrating existing data from

another table Typically, users will use applications with an

interface that allows data to be easily added/migrated, but programmers often need to write the INSERT statements ultimately executed by those applications

Two approaches Insert a value for every field Insert values for specific fields

Inserting Data

Inserting a value for every field Syntax

Example

INSERT INTO <table_name>VALUES (<value1>, <value2>, …);

INSERT INTO candy_productVALUES (1, ‘Celestial Cashew Crunch’, 7.45, 10);

Inserting Data

Inserting a value for every field Rules

You must include a value for every field You must list the values in the correct order

You can use DESCRIBE to find the correct order

With this syntax, the DBMS is expecting data for every field in a specific order

The data types must be consistent with the specified order

Otherwise an error occurs

DESCRIBE <table_name>;

Inserting Data

Inserting a value for specific fields Syntax

Example

INSERT INTO <table_name> (<field1>, <field2>,…)VALUES (<value1>, <value2>, …);

INSERT INTO candy_product (prod_desc, prod_id)VALUES (‘Celestial Cashew Crunch’, 1);

Inserting Data

Inserting a value for specific fields Rules

The field names can be specified in any order The corresponding values must be specified in

the same order as the specified field names If you are unsure of the values for all

fields, use this syntax Allows default column values to be used (if

specified for the corresponding field in the table)

Inserting Data

Specifying values Characters

Enclose values in single quotes (just like in SELECT query search conditions)

If a single quote should be present in the value, use two single quotes

Numbers Just specify the value (just like in SELECT query

search conditions)

Inserting Data

Specifying foreign key values You must insert the parent record first Otherwise, insert them just like other value

CUST_ID CUST_NAME CUST_TYPE_ID CUST_ADDR CUST_ZIP CUST_PHONE

1 Jones, Joe P 1234 Main St. 91212 434-1231

2 Armstrong,Inc. R 231 Globe Blvd. 91212 434-7664

3 Sw edish Burgers R 1889 20th N.E. 91213 434-9090

4 Pickled Pickles R 194 CityView 91289 324-8909

5 The Candy Kid W 2121 Main St. 91212 563-4545

6 Waterman, Al P 23 Yankee Blvd. 91234

7 Bobby Bon Bons R 12 Nichi Cres. 91212 434-9045

8 Crow sh, Elias P 7 77th Ave. 91211 434-0007

9 Montag, Susie P 981 Montview 91213 456-2091

10 Columberg Sw eets W 239 East Falls 91209 874-9092

PURCH_ID PROD_ID CUST_ID PURCH_DATEDELIVERY_DATEPOUNDS

1 1 5 28-Oct-04 28-Oct-04 3.5

2 2 6 28-Oct-04 30-Oct-04 15

3 1 9 28-Oct-04 28-Oct-04 2

4 3 9 28-Oct-04 28-Oct-04 3.7

5 3 2 28-Oct-04 2-Nov-04 3.7

6 1 7 29-Oct-04 29-Oct-04 3.7

7 2 7 29-Oct-04 29-Oct-04 1.2

8 3 7 29-Oct-04 29-Oct-04 4.4

9 2 6 29-Oct-04 30-Oct-04 3

10 2 10 29-Oct-04 31-Oct-04 14

11 5 10 29-Oct-04 2-Nov-04 4.8

12 1 4 29-Oct-04 29-Oct-04 1

13 5 4 29-Oct-04 30-Oct-04 7.6

14 5 3 29-Oct-04 29-Oct-04 3.5

Primary key Foreign key

Parentrecord

Childrecord

Inserting Data

How many parent records must be inserted and/or present in other tables before a record can be inserted into the candy_purchase table?a. 0b. 1c. 2d. 3e. None of the above

Inserting Data

Inserting dates Oracle and MySQL

Specify dates as strings in the expected format

Oracle Use the TO_DATE function

INSERT INTO <table_name> (<date_field>)VALUES (‘25-DEC-2014’);

INSERT INTO <table_name> (<date_field>)VALUES (‘2014-12-25’);

INSERT INTO <table_name> (<date_field>)VALUES (TO_DATE(‘2014-12-25 19:00:00’, ‘YYYY-MM-DD HH24:MI:SS’));

Format specifies the format of the date in the first argument

Oracle

MySQL

Inserting Data

Inserting dates MySQL

Remember that MySQL DATE types lack a time component

Use the DATETIME type for dates with a time component

Again, specify the date as a string in the expected formatINSERT INTO <table_name> (<date_field>)VALUES (‘2014-12-25 19:00:00’);

Overview

Inserting data Updating/deleting data Surrogate keys Transaction control

Updating Data

Syntax

Example

UPDATE <table_name>SET <field1> = <new_value>, <field2> = <new_value>, … <fieldN> = <new_value>WHERE <search_condition>;

UPDATE candy_productSET prod_price = 10.5, prod_cost = 7.50WHERE prod_id = 1;

Updating Data

Records can only be updated in one table at a time

Multiple records in the same table will be updated simultaneously if they match the search condition

When using Oracle SQL Developer or MySQL Workbench, if any part of the update fails, the entire update fails Not necessarily the case in other tools

(such as JDBC in Java applications)

Updating Data

Syntax

Example

DELETE FROM <table_name>WHERE <search_condition>;

DELETE FROM candy_purchaseWHERE purch_id = 9;

Deleting Data

Records can only be deleted in one table at a time

Multiple records in the same table will be deleted simultaneously if they match the search condition If the search condition is omitted, all records in the

table will be deleted A record cannot be deleted if one of its fields is

referenced as a foreign key in another table For tables with many records, it is quicker to drop

the table and recreate it than it is to delete all of its records

Deleting Data

How many total records must be deleted in order to delete the “Nuts Not Nachos” record from the candy_product table?

a. 1b. 2c. 3d. 4

Deleting Data

CASCADE DELETE Causes all child records to be automatically

deleted when a record in a parent table is deleted Option available in both Oracle and MySQL Applied to the foreign key constraint

Don’t use unless you’re absolutely sure that this behavior is desired

Example is Oracle syntax, MySQL syntax is similar, but without “CONSTRAINT <constraint_name>”

CREATE TABLE <table_name> ( <fk_field> <data_type>, CONSTRAINT <constraint_name> FOREIGN KEY (fk_field) REFERENCES <parent_table> (<parent_table_pk_field>) ON DELETE CASCADE);

Overview

Inserting data Updating/deleting data Surrogate keys Transaction control

Surrogate Keys

A surrogate key is a field created solely for the purpose of being a unique identifier in a databaseCUST_ID CUST_NAME CUST_TYPE_ID CUST_ADDR CUST_ZIP CUST_PHONE

1 Jones, Joe P 1234 Main St. 91212 434-1231

2 Armstrong,Inc. R 231 Globe Blvd. 91212 434-7664

3 Sw edish Burgers R 1889 20th N.E. 91213 434-9090

4 Pickled Pickles R 194 CityView 91289 324-8909

5 The Candy Kid W 2121 Main St. 91212 563-4545

6 Waterman, Al P 23 Yankee Blvd. 91234

7 Bobby Bon Bons R 12 Nichi Cres. 91212 434-9045

8 Crow sh, Elias P 7 77th Ave. 91211 434-0007

9 Montag, Susie P 981 Montview 91213 456-2091

10 Columberg Sw eets W 239 East Falls 91209 874-9092

Surrogate Keys

Their creation depends on the DBMS Oracle

Declare a NUMBER field as a primary key Create a “sequence” to automatically generate

sequential numbers This sequence is independent of the table Default sequence minimum value is 1

Use the sequence when inserting new records MySQL

Declare an integer primary key field with the AUTO_INCREMENT modifier

Surrogate Keys

Oracle Example

Other modifiable properties INCREMENT BY: allows sequence values to

increase by more than 1 MAXVALUE: specify a maximum sequence value CACHE: determine how many sequence values

are allocated when the sequence is used (allows for faster access)

CREATE TABLE candy_product( prod_id NUMBER(6) CONSTRAINT candy_product_id_pk PRIMARY KEY, prod_desc VARCHAR2(30), prod_cost NUMBER(4,2), prod_price NUMBER(4,2));

CREATE SEQUENCE candy_product_seq MINVALUE 0;

Surrogate Keys

MySQL Example

CREATE TABLE candy_product( prod_id INT(6) PRIMARY KEY AUTO_INCREMENT, prod_desc VARCHAR(30), prod_cost DECIMAL(4,2), prod_price DECIMAL(4,2));

Surrogate Keys

Using surrogate keys in Oracle Use the sequence’s NEXTVAL to obtain the next

value

Use the sequence’s CURRVAL to obtain the current value

CURRVAL is useful when inserting values for foreign keys that reference primary keys inserted immediately prior

It will access the most recently generated surrogate key by that sequence in the current session

INSERT INTO candy_purchase (purch_id, prod_id, cust_id)VALUES(purch_id_sequence.NEXTVAL, candy_customer_seq.CURRVAL, candy_product_seq.CURRVAL);

INSERT INTO candy_product (prod_id)VALUES (candy_product_seq.NEXTVAL);

INSERT INTO candy_customer (cust_id)VALUES (candy_customer_seq.NEXTVAL);

Surrogate Keys

Using surrogate keys in MySQL Using the “inserting values for specific fields”

approach

Using the “inserting values for all fields” approach

The AUTO_INCREMENT modifier will automatically generate and apply the surrogate key value for the corresponding record Use null or 0 if specifying a value for the

AUTO_INCREMENT key

INSERT INTO candy_customer(cust_name, cust_type, cust_addr)VALUES (‘Bobby Bon Bons’, ‘R’, ‘12 NichiCres.’);

INSERT INTO candy_productVALUES (null, ‘Celestial Cashew Crunch’, 7.45, 10);

Surrogate Keys

Using surrogate keys in MySQL Use the LAST_INSERT_ID() function to retrieve the most

recently AUTO_INCREMENT generated surrogate key value for any table for the current session

Assumptions purch_id is an AUTO_INCREMENT field and we want to

recognize a new purchase A new customer and product were just inserted (previous

slide) in that order using AUTO_INCREMENT (with ascending increments)

We are confident that no customers have been inserted since Bobby Bon Bons (risky)

Better to programmatically store the most recently added cust_id

INSERT INTO candy_purchase (prod_id, cust_id)VALUES(LAST_INSERT_ID(), (SELECT MAX(cust_id) FROM candy_customer));

Surrogate Keys

Oracle sequence concerns Sequences are not explicitly connected to a table

Sequences can be referenced by multiple tables If a sequence’s NEXTVAL is called and the value

obtained is not inserted, then that value is lost If multiple users access a sequence that has a

CACHE value (must be at least 2), then those sequence values are reserved and may be lost if not used

If a surrogate key value is hardcoded in an insert statement instead of using the sequence, the sequence may later produce the same value

Surrogate Keys

MySQL AUTO_INCREMENT concerns Limited to one column per table Assigned to a specific table (cannot be

used across tables as in Oracle) If a surrogate key value is hardcoded in an

insert statement instead of using the AUTO_INCREMENT, AUTO_INCREMENT will recognize it

If transactions are rolled back, gaps in AUTO_INCREMENT values may be present

Overview

Inserting data Updating/deleting data Surrogate keys Transaction control

Transaction Control

A transaction is a logical unit of work that might involve multiple action queries Examples

Withdrawing money from one bank account and depositing it into a different account

Booking a seat on an airplane All of the action queries in a transaction

must succeed or none of them should succeed Applies to INSERT, UPDATE, and DELETE

statements, but not to SELECT statements (since they don’t modify the database)

Transaction Control

A transaction can be explicitly started using the START TRANSACTION command

All subsequent action queries will belong to the same transaction until the transaction is committed

A transaction can be explicitly committed using the COMMIT command

Use the ROLLBACK command to “undo” all action queries in the current transaction (since the last commit)

COMMIT;

START TRANSACTION;

ROLLBACK;

Transaction Control

Oracle SQL Developer By default, implicit transaction control is

used The transaction starts when you connect to the

database, and commits when you tell it to (either via the commit button or the COMMIT command)

Database changes wouldn’t be visible to other users until they’re committed

After a commit, the next command automatically starts a new transaction

You should be prompted to commit any uncommitted transactions when quitting the application

Transaction Control

MySQL Workbench No implicit transaction control Example with auto commit off

-- 1 --INSERT INTO candy_product VALUES(null, 'test1', 1, 2);-- 2 --SELECT * FROM candy_product;

Connection 1

Connection 2

-- 3 –-SELECT * FROM candy_product;-- prod_id 7 not shown-- not committed by Connection 1

Transaction Control

MySQL Workbench with auto commit off

-- 1 --INSERT INTO candy_product VALUES(null, 'test1', 1, 2);-- 2 –-SELECT * FROM candy_product;-- prod_id 7 is shown

-- 4 --COMMIT;

Connection 1

-- 3 --SELECT * FROM candy_product;-- prod_id 7 not shown

-- 5 –-SELECT * FROM candy_product;-- prod_id 7 still not shown

-- 6 --COMMIT;-- 7 --SELECT * FROM candy_product;-- prod_id 7 now shown

Connection 2

This SELECT operation started a transaction and later SELECTs won't show changes until COMMIT from connection 1 AND connection2

Transaction Control

Oracle SQL Developer in same scenario

-- 1 --INSERT INTO candy_product VALUES(null, 'test1', 1, 2);-- 2 –-SELECT * FROM candy_product;-- prod_id 7 is shown

-- 4 --COMMIT;

Connection 1

-- 3 --SELECT * FROM candy_product;-- prod_id 7 not shown

-- 5 –-SELECT * FROM candy_product;-- prod_id 7 is shown

Connection 2

Not necessary to commit from connection 2 to see committed changes from connection 1

Transaction Control

Implications due to transactions Before a transaction is committed, its

actions are visible on your connection but not to others

When a transaction is committed, it cannot be rolled back, and its changes may be visible to other users

By default, most applications that interact with a database will auto commit transactions