1 oracle quiz on sql and pl/sql – see water burning oracle quiz on sql and pl/sql see water...

1Oracle Quiz on SQL and PL/SQL – See water burning

Oracle Quiz on SQL and PL/SQL

See water burning

Alex Nuijten & Lucas JellemaAMIS, The Netherlands


Journey to the Mythical Heart of the Matter...

We will look at some lesser known Oracle SQL and PL/SQL features And see some ..ahem… alternative usages of well

known features

In the form of a Quiz, you can show off Multiple choice, no modifications, play fair! Winner gets to select any book from the bookstall


What is the name of Scott’s cat?

A. King

B. Tiger

C. Big Red

D. Bruce

1


The Demo-tables – The Infamous SCOTT schema


What has been done to have this query return this result?

A. Data in EMP have been manipulated

B. 10g Package DBMS_ADVANCED_REWRITE has been (ab)used

C. Pre-parsed cursor fetch has been rolled over by buffer- cache checkpoint high water mark

D. 9iR2 and beyond query randomizer at work

2


What is the result of this query?

A. OPERATIONS

B. New York

C. 04

D. SELAS

3


Which query implements this question?

For all employees, return the name and If they are manager

• And their salary is 2950 or up, return label ‘High’• Salary under 2950, return label ‘Low’

Else, in case they are not a manager, return• label ‘Low’ if they earn under 1000• label ‘Medium Odd’ if they have an odd salary over 1000• label ‘Medium’ if their salary is over 1000 and it is an even

number


Which query implements this question?

A. B.

D.C.

4


CASE offers a much more attractive solution:


DECODE vs. CASE

Why not DECODE Hard to read, impossible to maintain Not part of the ANSI standards for SQL CASE expressions are a lot more powerful

When/Where CASE: In SQL

• select, where, having, order by

In PL/SQL In Check Constraints In Index definitions


How can we implement this business rule?

A department may not have more than one CLERK

A. Unique Constraint - on EMP (DEPTNO, JOB)

B. Check Constraint with CASE expression

C. Unique Index

D. Insert and Update trigger on EMP (column DEPTNO and JOB)

5


Function Based Unique Index

An index can be defined as UNIQUE A UNIQUE index ignores NULL-clashes

UNIQUE (deptno, job) accepts (NULL,NULL) and (NULL,NULL)

A Function Based Index can be defined for an expression or PL/SQL function call, for example a CASE expression

A department may not have more than one CLERK:


How do we make a random selection of approximately 10% of our Employee records?

A. B.

D.C.

6


FROM … SAMPLE (8i)

FROM <table> sample (percentage)

The sample_clause lets you instruct Oracle to select from a random sample of rows from the table, rather than from the entire table. The sample percentage is between 0.000001 and 100 The percentage indicates the chance for each record

to be included in the sample

select emp.*, dept.dnamefrom emp sample (10) -- 10%, deptwhere emp.deptno = dept.deptno


Whoops Management

I perform this update: update emp set sal = (1+ dbms_random.value) * sal;

commit; Whoops….production system… Oh Oh.

How can I best correct this situation?

A. Flashback Database and Roll Forward until just prior to the update

B. Select old values from Flashback Query and update

C. Restore a database backup, export table and import

D. Use the 10g ‘Undo Transaction’ statement

7


Flashback Query

select * from table AS OF TIMESTAMP Select values as they were at a certain moment

in time Depends on UNDO data In actual fact is every Oracle query (due to the read-

consistency) some sort of flashback query)


The Top-3 Earning Employees

What can you state about the query below with regard to the quest for the “Top 3 earning employees”?

A. Returns the correct answer

B. May sometimes return the correct answer

C. Okay as long as there are no duplicate salaries

D. Not correct

8


In-Line Views

In line views have been around since 7.2 (and in 7.1 an undocumented feature)


Can we select the Top 3 Earners PER DEPARTMENT?

A. B.

D.

C.

Can not be done in a single Query

9


Analytical Functions


SELECT … ANALYTICAL FUNCTION (8i/9i)

Functions for advanced analysis OLAP inspired Very efficient compared to traditional SQL Since 8.1.7 EE and 9iR2 SE

Typical Analytical operations Aggregation Ranking Deduplication Inter-row comparisons and calculations

• Spreadsheet-ish

Statistical Analysis


Which of these queries contains an invalid Oracle 9iR2 SQL-statement

A. B.

D.C.

10


User Defined Aggregate

Oracle Data Cartridge allows us to define our own Aggregates For example:

SUM_VARCHAR2, AVG_DATE,COUNT_CHARACTERS

select avg(hiredate) from emp

ORA-00932: inconsistent datatypes: expected NUMBER got DATE


User defined sum_varchar2 aggregate

Implement AmisVarchar2SumImpl object Create function sum_varchar2 as aggregate

using object AmisVarchar2SumImpl

select deptno, sum_varchar2(ename) employeesfrom empgroupby deptno


What is going on here?

A. Table Function and UTL_FILE

B. External Table

C. Materialized View

D. REDO LogFile

Plaatje EXCEL

11


CREATE TABLE emp_ext ( empcode NUMBER(4), empname VARCHAR2(25), deptname VARCHAR2(25), hiredate date ) ORGANIZATION EXTERNAL ...

EXTERNAL TABLE (9i)

Data in an external text-file can be published as ‘table’ in the database accessed in SQL and PL/SQL like a normal table

Define table with ORGANIZATION EXTERNAL

ExternalTables select *

from …where …


Language!?


What (or who) is behind all this?

A. View on Table Function that generates of transforms values

B. NLS_RESOURCE_BUNDLE settings

C. Virtual Private Database – policy function on table

D. View with PL/SQL Function Call in the WHERE-clause

12


FROM … TABLE FUNCTION (9i)

(result returned by) PL/SQL Function can be used as data-source in query As if it were a table

Function must return a Server NESTED TABLE Type • CREATE TYPE NUM_TABLE IS TABLE OF NUMBER

Functions can be nested, parallelized and/or pipelined

... from table( function(<parameters) )where ...


PieCharts in SQL

Can you have a SQL query return apie chart? For example to review the salary sums

per JOB catagory

A. No. Are you out of your mind?

B. I would be surprised. I assume with Table Functions…

C. Piece of cake (pun intentional) : use the new 10g EXTRACT_PIE function

D. Yeah, you can do that, but only on Windows

13


PieChart in SQL


Final scores….

How many correct answers did you give?

A, C or D

13

12

11

101

2

3

4

5

6

7

8

9

B

B

D

A

C or D

B or D

B (a or c)

B or D

D (c)

A

B or A

B


… and the winner is…


How often will this trigger fire for this update statement?

A. No more than 3 times

B. Up to 5 times

C. At least three with a maximum of 6 times

D. Unlimited


What is happening?

Session 1 Session 2

update i=1, i=2 and begin with i=3; run into lock held

by session 2

updates are rolled-back and a select-

for update is initiated

The lock on i=3 is released now; i

equals 6!


Which Country is The Netherlands?

1 oracle quiz on sql and pl/sql – see water burning oracle quiz on sql and pl/sql see water...

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