Database Programming Sections 7–Multi-row sub queries, IN, ANY, ALL, Data Manipulation Language (DML) transaction, INSERT, implicit, explicit, USER, UPDATE,

Database Programming

Sections 7–Multi-row sub queries, IN, ANY, ALL, Data Manipulation Language (DML) transaction, INSERT, implicit, explicit, USER, UPDATE, DELETE, integrity constraint, Parent record, Child record

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Multi-row subquery

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7.1.4 Example

Write a query to find the name of the Global Fast Foods employee who makes the most money?

Solution next slide

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Solution using subquery

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Multiple-Row Subqueries Subqueries that return more than one value

are called multiple-row subqueries When used in a WHERE clause, the

multiple-row subquery must use a multiple-row operator, such as IN, ANY, or ALL.

The multiple-row operators are:IN ANY ALL

The NOT operator can be used with any of these three operatorsSee example on next slide

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Multiple-Row Subqueries cont’d

SELECT employee_id, last_name, salary, department_idFROM employeesWHERE salary NOT IN (SELECT salary FROM employees WHERE last_name = ‘King’);

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IN SELECT

last_name,salary, department_idFROM employeesWhere salary IN(SELECT MIN(salary) FROM employees GROUP BY department_id);

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ANY The ANY operator compares a value to each

value returned by a subquery. SELECT employee_id, last_name, job_id,

salaryFROM employeesWHERE salary < ANY (SELECT salary FROM employees WHERE job_id = ‘IT_PROG’);

Results next slide

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Results of ANY

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All Used when the outer-

query WHERE clause is designed to restrict rows based on all values returned from the inner query.

the inner query will return a list of values.

The ALL operator compares a value to every value returned by the inner query.

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NULL Values in Subqueries

SELECT emp.last_nameFROM employees empWHERE emp.employee_id NOT IN (SELECT mgr.manager_id FROM employees mgr);

SQL Query ResultsNo DataOne of the values returned by the inner query is a null value, and hence the entire query returns no rows. King does not have a manager.

MANAGER_ID

-

100

100

102

103

103

100

124

124

124

124

100

149

149

149

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NULL Example SELECT department_id, department_name

FROM departmentsWHERE department_id = (SELECT department_id FROM employees WHERE salary >60000);

SQL Query Results. No data found. No employee has a salary >60000 There is no such thing as = NULL as NULL is not

zero!

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Null Values in Subqueries, cont’d

SELECT emp.last_nameFROM employees empWHERE emp.employee_id NOT IN (SELECT mgr.manager_id FROM employees mgr WHERE mgr.manager_id IS NOT NULL);

View results of inner query on next slide. Now, none of the values returned by the inner

query is a null value, thus it works.

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Results of Inner Query

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Examples 7.2.4 1. Select all the employees (name, job ID,

salary) in departments 10 and 30. Write two different queries that will produce the desired result.

2. Select the name of all the departments (department name and location id) and order by department number. Do not display the department number in the output.

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Possible Answers 7.2.41.

a. SELECT last_name,job_id, salary FROM employees WHERE department_id in (10,30);

b. SELECT last_name,job_id, salary FROM employees WHERE department_id = 10 or department_id=30;

c. This is not the most efficient answer, but it does return the correct results:SELECT last_name,job_id,salary FROM employees WHERE department_id IN(            SELECT department_id             FROM departments            WHERE department_id IN (10,30));

2. SELECT department_name, location_id FROM departments ORDER BY department_id;

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Overview of remainder of lesson Data Manipulation

Language DML INSERT UPDATE DELETE MERGE

Default Values Merge Statements Creating Tables Using Data Types

Data Definition Language DDL ALTER TABLE DROP TABLE RENAME TRUNCATE COMMENT

Define Constraints Manage

Constraints

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Using a subquery to copy a table

In order to experiment with the tables, make a copy of them:Select all rows from the EMPLOYEES table and insert them into the COPY_EMPLOYEES table. CREATE TABLE copy_employees

AS (SELECT * FROM employees); Verify by:

SELECT *FROM copy_employees;

the integrity rules (primary keys, default values are not passed to the copy, only the column datatype definitions.)

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Explicitly inserting data The INSERT statement is used to add new rows to a

table. To get the column names and default order, use:

The statement requires three values: the name of the table the name of the column in the table to populate a corresponding value for the column –

INSERT INTO copy_departments (department_id, department_name, manager_id, location_id)VALUES (70,’Public Relations’, 100, 1700);

INSERT INTO copy_departments (department_id, manager_id, location_id, department_name)VALUES (99, 100, 1700, ‘Advertising’)

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Implicitly inserting data

Omit the column names Match exactly the default order in

which columns appear in the table Provide a value for each column. INSERT INTO copy_departments

VALUES (100,’Education’, 100, 1700); using VALUES adds on row at a time

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Insert with NULL values Implicit Method – omit the column from the column

list Any column that is not listed obtains a null value in

the new row – errors can occur – the row has been specified NOT NULL, uniqueness, foreign key violation

INSERT INTO copy_departments (department_id, department_name)VALUES (30,’Purchasing’);

Explicit Method – specify the NULL keyword in the values clause INSERT INTO copy_departments

VALUES (100, ‘finance’, NULL, NULL);

DEPARTMENT_ID DEPARTMENT_NAME MANAGER_ID LOCATION_ID 100 Finance - -

30 Purchasing - -

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Inserting Special Values Special values such as SYSDATE and USER can be

entered in the VALUES list of an INSERT statement. SYSDATE puts current date in a column USER places current username (HTML DB will put

HTMLDB_PUBLIC_USER) INSERT INTO copy_employees (employee_id,

last_name, email, hire_date,job_id)VALUES(1001, USER, ‘Test’ SYSDATE, ‘IT_PROG’);

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Inserting Specific date values The default date before Oracle 9i was DD-

MON-YY. The default format for Oracle 9i is DD-MON-

RR century defaults to the current century default time of midnight (00:00:00) formats other than the default format use

TO_DATE function INSERT INTO copy_employees

VALUES (114, ‘Den’, ‘Raphealy’, ‘DRAPHEAL’, ‘515.127.4561’, ’03-FEB-49’, ‘AC_ACCOUNT’, 11000, NULL, 100, 30);

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Date Example INSERT INTO copy_employees

VALUES (114, ‘Den’, ‘Raphealy’, ‘DRAPHEAL’, ‘515.127.4561’, ’03-FEB-49’, ‘AC_ACCOUNT’, 11000, NULL, 100, 30);

SELECT last_name, TO_CHAR(hire_date, ’Month dd, RRRR’)FROM copy_employeesWHERE employee_id = 114;

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Using a subquery to copy rows Copy values from an existing table

CREATE TABLE sales_reps(id number(5), name varchar2(15), salary number(10), commission_pct number (8));

No VALUES clauseINSERT INTO sales_reps(id, name, salary, commission_pct) SELECT employee_id, last_name, salary, commission_pct FROM employees WHERE job_id LIKE ‘%REP%’;

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UPDATE statements The UPDATE statement is used to modify

existing rows in a table. It requires four values: the name of the table

UPDATE copy_employees the name of the column in the table to populate

SET department_id a corresponding value or subquery for the

column SET department_id = 70

a condition that identifies the columns and the changes for each column WHERE employee_id = 113;

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Updating one column Specific row or rows are modified if you

specify the WHERE clause. UPDATE copy_employees

SET department_id = 70WHERE employee_id = 113;(One row is updated)

All rows in the table are modified if you omit the WHERE clause. UPDATE copy_employees

SET department_id = 110;(All rows are updated)

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Update using subquery

UPDATE copy_employeesSET department_id = (SELECT department_id FROM employees WHERE last_name = ‘Ernest’)WHERE employee_id = 113;

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Updating columns with subqueries You can update one or more columns in the

SET clause of an UPDATE statement by writing subqueries.

UPDATE copy_employeesSET job_id = (SELECT jobt_id FROM employees WHERE employee_id =205) salary = (SELECT salary FROM employees WHERE employee_id =205)WHERE employee_id = 114;

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Integrity Constraints Integrity constraints define certain data quality

requirements that the data in the database needs to meet. If a user tries to insert data that doesn’t meet these requirements an error will occur.

Types of Integrity constraints NOT NULL – each row in the column must have a value PRIMARY KEY – unique and not null FOREIGN KEY – A foreign key constraint (also called

referential integrity constraint) on a column ensures that the value in that column is found in the primary key of another table.

CHECK – value meets certain conditions salary CHECK < 50000

UNIQUE – no duplicate values in a column (email address)

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Integrity Constraint Errors UPDATE employees

SET department_id = 55WHERE department_id = 110;

ORA-02291: integrity constraint(USCA_INST_SQL03_T01.EMP_DEPT_FK) violated – parent key not found

There is no department_id = 55 in the departments table which is the parent table

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DELETE statement

The DELETE statement is used to remove existing rows in a table. The statement requires two values: the name of the table the condition that identifies the rows to

be deletedDELETE *FROM copy_employeesWHERE employee_id = 200;

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Subquery Delete Use subqueries in DELETE statements

to remove rows from a table based on values from another table.

DELETE FROM copy_employeesWHERE department_id = (SELECT department_id FROM departments WHERE department_name LIKE ‘%REP%’);

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Default Values A column in a table can be given a default

value. Assigning default values prevents null

values from existing in the column. Default values can be:

a literal value ‘no commission assigned’ an expression salary*1.15 SQL function, such as SYSDATE or USER

Default values must match the data type of the column

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Default Values Examples Default Values Specified as the time the

table is created:CREATE TABLE items( part_number VARCHAR2(10), description VARCHAR2(10), qty_on_hand NUMBER DEFAULT 0);

INSERT INTO items(part_number, description)VALUES (‘AB154’,’hammer’);

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Default Values - Examples Use DEFAULT when inserting values:

INSERT INTO items(part_number, description, qty_on_hand)VALUES (300,’Widger’, DEFAULT);

Use DEFAULT when updating values: UPDATE items

SET qty_on_hand = DEFAULTWHERE part_number = 200;

Now check the results! SELECT *

FROM items;

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MERGE MERGE Statement

Accomplishes an UPDATE and INSERT at the same time ** the ON clause specifies the match – if two id’s match make the following updates, otherwise insert the following as new rows

MERGE INTO copy_emp c USING employees e ON (c.employee_id = e.employee_id)WHEN MATCH THEN UPDATE SET c.first_name = e.first_name c.last_name = e.last_name ..... c.department_id = e.department_idWHEN NOT MATCHED THEN INSERT VALUES( e.employee_id, e.first_name, e.last_name, e.salary, e.commission_pct, e.manager_id, e.department_id);

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MERGE Example: MERGE INTO copy_items c USING

items i ON(c.part_number = i.part_number)WHEN MATCHED THEN UPDATE SETc.description = i.descriptionc.qty_on_hand = i.qty_on_handWHEN NOT MATCHED THEN INSERT VALUES(i.part_number, i.description, i.qty_on_hand);

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CREATING TABLES

Naming Rules: Must begin with a letter Must be 1 to 30 characters in length Must only contain alpha/numeric,_,$,# Must be unique Must not be an Oracle Server reserved

word

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Using Data Types

Most Common Data Types: VARCHAR2

Examples: Name, Address NUMBER

Examples: Price, Quatity DATE

Examples: DOB, Hire Date

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Creating Tables CREATE TABLE name

(column name DATATYPE(specifications for datatype) VARCHAR2(number of characters) – variable

length data 1-4000 CHAR(size) – fixed length data 1-2000 NUMBER(precision, scale) – total number of

decimal digits(1 to 38), right of decimal digits(-84 to 127) For example, a scale of 2 means the value is rounded to the nearest hundredth (3.456 becomes 3.46); a scale of -3 means the number is rounded to the nearest thousand (3456 becomes 3000).

DATE – date and time

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Creating Tables cont’d

CREATE TABLE students(id, VARCHAR2(5), lname VARCHAR2(15), fname VARCHAR2(15), GPA number(6), enroll_date date DEFAULT SYSDATE);

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ORACLE Data Dictionary The data dictionary is a collection of tables created and

maintained by the Oracle Server and contains information about the database.

All data dictionary tables are owned by the SYS user. Because the tables are difficult to understand, users access data dictionary includes names of the Oracle Server users, privileges granted to users, database object names, table constrains and auditing information.

You may browse the Oracle Data Dictionary to show objects you own. SELECT *

FROM DICTIONARY; - returns 610 items SELECT table_name

FROM user_tables; SELECT DISTINCT object_type

FROM user_objects; SELECT *

FROM user_catalog;

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Using Interval Year to Month INTERVAL YEAR TO MONTH: Stores a period of time in

years/monthsNote that the argument 3 in the create table and insert statements refers to precision

CREATE TABLE time_ex2(school_year_duration INTERVAL YEARS(3) TO MONTH);

INSERT INTO time_ex2(school_year_duration)VALUES(INTERVAL ‘9’ Month(3));

SELECT TO_CHAR(SYSDATE + school_year_duration, ‘dd-Mon-yyyy’)FROM time_ex2;

Returned 9 month from today’s date

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USING INTERVAL DAY TO SECOND

INTERVAL DAY TO SECOND: Stores a more precise period of time (days/hours/minutes/seconds) CREATE TABLE time_ex3(day_duration

INTERVAL DAY(3) to SECOND); INSERT INTO time_ex3(day_duration)

VALUES(INTERVAL ‘180’ DAY(3)); SELECT SYSDATE + day_duration “Half

Year” FROM time_ex3;

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Using Time Data Types

TIMESTAMP: stores values with respect to universal time CREATE TABLE time_example

(order_date TIMESTAMP WITH LOCAL TIME ZONE,ship_date DATE DEFAULT SYSDATE);

INSERT INTO time_exampleVALUES(SYSDATE, SYSDATE);

SELECT *FROM time_example;