IST 210 More SQL

Todd BacastowIST 210: Organization of Data

IST 210 Simple JoinConsider:

Likes (drinker, beer)Sells (bar, beer, price)

SELECT drinker, barFROM Likes, SellsWHERE Likes.beer=Sells.beer;

What’s happening here????

IST 210 Examples

Employees:

Employee_IDName

01 Hansen, John

02 Shara, Tove

03 Seven, Stephen

04 Pettersen, Kari

Orders:

Prod_IDProduct Employee_ID

234 Printer 01

657 Table 03

865 Chair 03

IST 210

Who has ordered a product, and what did they order?

SELECT Employees.Name, Orders.Product FROM Employees, Orders WHERE Employees.Employee_ID=Orders.Employee_ID

Result

NameProduct

Hansen, John Printer

Seven, Stephen Table

Seven, Stephen Chair

IST 210 Who ordered a printer?

SELECT Employees.Name FROM Employees, Orders WHERE Employees.Employee_ID=Orders.Employee_ID AND Orders.Product='Printer'

Result

Name

Hansen, John

IST 210 Other ‘Joins’ in SQL2 R NATURAL JOIN S R CROSS JOIN S R JOIN S ON condition R OUTER JOIN S R INNER JOIN S

IST 210 Alternative JOIN Constructs SQL2 provides alternative ways to specify joins:

SELECT * FROM Likes.beer JOIN Sells.beer ON Likes.beer= Sells.beer

SELECT * FROM Likes JOIN Sells USING beer

SELECT * FROM Likes NATURAL JOIN Sells

The first produces a table with two identical beer columns, remaining two produce table with single beer column.

IST 210 Outer Join Outerjoin = natural join with dangling tuples

padded with NULLs and included in the result A tuple is dangling if it doesn’t join with any

other tuple

A B

1 2

3 4

B C

2 5

2 6

7 8

A B C

1 2 5

1 2 6

3 4 NULL

NULL

7 8

OUTERJOIN =

IST 210 Modifiers of OUTER JOIN Optional NATURAL in front Optional ON condition at end Optional LEFT, RIGHT, FULL

before OUTER LEFT = Pad dangling tuples of R ONLY RIGHT = Pad dangling tuples of S

ONLY

IST 210 Inner Join

SELECT Employees.Name, Orders.Product FROM Employees INNER JOIN Orders ON Employees.Employee_ID=Orders.Employee_ID

NameProduct

Hansen, John Printer

Seven, Stephen Table

Seven, Stephen Chair

Result

The INNER JOIN returns all rows from both tables where there is a match. If there are rows in Employees that do not have matches in Orders, those rows will not be listed. EXAMPLE: Who has ordered a product, and what did they order?

IST 210 Calculated Fields Query

Produce a list of monthly salaries for all staff, showing the staff number, the first and last names, and the salary details.

SELECT sno, fname, lname, salary/12

FROM staff;To name column, use AS clause:

SELECT sno, fname, lname, salary/12 AS monthly_salary

FROM staff;

Monthly_salary

IST 210 Range Search Condition - BETWEEN

Query:List all staff with a salary between

20,000 and 30,000.

SELECT sno, fname, lname, position, salaryFROM staffWHERE salary BETWEEN 20000 AND 30000;

IST 210

Range Search Condition (Cont…)

BETWEEN test includes the endpoints of range. Equivalent to

SELECT sno, fname, lname, position, salaryFROM staffWHERE salary>=20000 AND salary <= 30000;

BETWEEN does not add much to SQL's expressive power

Also a negated version NOT BETWEEN.

IST 210

Set Membership - IN / NOT IN Query: List all Managers and Deputy

Managers.

SELECT sno, fname, lname, position

FROM staffWHERE position IN ('Manager', 'Deputy');

IST 210 Pattern Matching - LIKE SQL has two special pattern matching symbols:

%: sequence of zero or more characters; _ (underscore): any single character.

LIKE '%Glasgow%' means a sequence of characters of any length containing 'Glasgow'.

Query: Find all staff with the string 'Glasgow' in their address.

SELECT sno, fname, lname, address, salaryFROM staffWHERE address LIKE '%Glasgow%';

IST 210 NULL Search Condition NULL value can not be checked by comparison

operators Have to test for null explicitly using special

keyword IS NULL IS NOT NULL can test for non-null values. Example query:

List details of all viewings on property PG4 where a comment has not been supplied.

SELECT rno, dateFROM viewingWHERE pno = 'PG4' AND

comment IS NULL;

IST 210 ORDER BY Example Query:

List salaries for all staff, arranged in descending order of salary.

SELECT sno, fname, lname, salaryFROM staffORDER BY salary DESC;

When no (ASC/DESC) is indicated, default order is ascending (ASC).

Can sort on multiple columns.SELECT pno, type, rooms, rentFROM property_for_rentORDER BY type, rent DESC;

IST 210 GROUP BY and HAVING Use GROUP BY clause to get sub-totals. SELECT and GROUP BY closely integrated: each item in

SELECT list must be single-valued per group, and SELECT clause may only contain:

Column names. Aggregate functions. Constants. An expression involving combinations of the above.

If WHERE is used with GROUP BY, WHERE is applied first, then groups are formed from remaining rows satisfying predicate.

Considers two nulls to be equal for purposes of GROUP BY.

IST 210

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Use of GROUP BY

Example: Find number of staff in each branch and their total salaries.

SELECT bno, COUNT(sno) AS count, SUM(salary) AS sumFROM staffGROUP BY bnoORDER BY bno;

IST 210 Restricted Grouping - HAVING HAVING clause is designed for use with GROUP BY

clause to restrict groups that appear in final result table. HAVING filters groups. Column names in HAVING clause must also appear in

the GROUP BY list or be contained within an aggregate function.

Example: For each branch with more than 1 member of staff, find number of staff in each branch and sum of their salaries.

SELECT bno, COUNT(sno) AS count, SUM(salary) AS sumFROM staffGROUP BY bno HAVING COUNT(sno) > 1ORDER BY bno;

IST 210 Subquery with Aggregate Example: List all staff whose salary is greater than the average

salary.

SELECT sno, fname, lname, position, salaryFROM staffWHERE salary >

(SELECT avg(salary) FROM staff);

Cannot write 'WHERE salary > avg(salary)' Instead, use subquery to find average salary (17000), and then

use outer SELECT to find those staff with salary greater than 17000

Subquery SELECT list must consist of a single column name or expression, except for subqueries that use EXISTS.

IST 210 ANY/SOME and ALL If subquery preceded by ALL, condition will

only be true if it is satisfied by all values produced by subquery.

If subquery preceded by ANY, condition will be true if it is satisfied by any values produced by subquery.

If subquery is empty, ALL returns true, ANY returns false.

IST 210 Example of ANY and ALL Example1: Find staff whose salary is larger than salary of at least

1 member of staff at branch B3.SELECT sno, fname, lname, position, salaryFROM staffWHERE salary >ANY

(SELECT salary FROM staff WHERE bno = 'B3');

Example 2: Find staff whose salary is larger than salary of every member of staff at branch B3.

SELECT sno, fname, lname, position, salaryFROM staffWHERE salary > ALL

(SELECT salary FROM staff WHERE bno = 'B3');

IST 210 Sorting a join Consider: For each branch, list

names of staff who manage properties.

SELECT s.bno, s.sno, fname, lname, pnoFROM staff s, property_for_rent pWHERE s.sno = p.snoORDER BY s.bno, s.sno, pno;