IST 318 – DB Administration

Data Retrieval

Using SELECT statements

Data Modeling

Entity: something exists and can be describedAttribute: a characteristic of an entity

Describes: most attributes play this role Identifies: PK (or any other attr that is unique) Relates: FK

Relationship: shows how entities associated with each other May also have descriptive attributes

ER Diagrams

Notations for Entities: boxes Attributes and keys (PK, FK)

Notations for Relationships: diamonds/lines Constraints

Cardinality: 1:1, 1:M, M:1, M:N Optionality

• Mandatory: 1, 1..M

• Optional: 0..1, 0..M

Conversion from ERM to Tables

Entities and relationships will be converted into tables in design One entity one table

Attribute column Domain data type Value range range constraints

M:N Relationship one table

SELECT Statement: basic structure

SELECT – specifying what to displayFROM – specifying where data come fromWHERE – specifying criteria for individual

recordsGROUP BY – specifying how to divide records

into groupsHaving – specifying criteria for groups ORDER BY – specifying the way to sort results

SELECT Clause

May include columns or expressionsExpressions may include

Arithmetic operations Single-row functions (maybe nested) Group functions (maybe nested up to 2 levels)

Columns/expressions may be displayed using (column) aliases Alias may be quoted with “” (double quotes) AS keyword optional

FROM Clause

Include tables or views (to be discussed later)

Table aliases may be used Once used, original table names may not be

used to qualify columns in WHERE clause

Two syntax styles Traditional: list table names directly, separated

with colons (,) Standard: using JOIN syntax (to be specified on

separate slides)

WHERE Clause

Logical operators may be used to build composite conditions AND, OR, NOT

Relational operators: =, <>/!=/^=, >, <, ... IN (.., ..)BETWEEN ... AND ...IS NULL/IS NOT NULLLIKE

GROUP BY Clause

May include columns or expressions Expressions may not include group functions Columns/expressions appeared in SELECT

clause together with expressions w/ group functions must also appear here. But not the other way round.

May not use column aliases hereWill be carried out after criteria in the

WHERE clause are applied

HAVING Clause

May only use expressions with group functions

May appear before or after the GROUP BY clause

ORDER BY Clause

Columns/expressions used here don’t have to appear in the SELECT clause

May sort to ascending (default) or descending order May use multiple col/expr to sort, each to a

different order

May sort by column aliases or location in the SELECT clause as well

Matching String Patterns

Use the LIKE operator, instead of = May use NOT LIKE

Wildcard matching characters _ : representing exactly one character/digit % : represent any (0 .. many) characters

It is CASE-SENSITIVE Use case manipulation functions to match up

WHERE upper(course#) like ‘IST%’

Single-Row Functions: for char

substr(col, start, length) substr(col, -start, length): starting from the end

trim()length()ltrim/rtrimlpad/rpad(col, length, c)

Single-Row Functions: for number

trunc(col, p) p > 0 p = 0 p < 0

round(col, p)

Single-Row Functions: Type Conversion

to_char(number, ‘L9,999.99’) L is for local currency $ may be used

to_char(date, 'fmMM/DD/YYYY') SELECT to_char(sysdate, 'fmMM/DD/YYYY‘)

FROM dual

Single-Row Functions: Generic

nvl(col, vn)nvl2(col, vnn, vn)case

SELECT last_name, job_id, salary, CASE job_id WHEN 'IT_PROG' THEN 1.10*salary WHEN 'ST_CLERK' THEN 1.15*salary WHEN 'SA_REP' THEN 1.20*salary ELSE salary END "REVISED_SALARY"FROM employees;

Single-Row Functions: DECOE

SELECT last_name, job_id, salary, DECODE(job_id, 'IT_PROG', 1.10*salary, 'ST_CLERK', 1.15*salary, 'SA_REP', 1.20*salary, salary) REVISED_SALARYFROM employees;

Nested Group Function

2-level topsGroup by clause has to be usedNo other expressions without nested

group functions allowed to show in the same SELECT clause SELECT max(avg(retail))

FROM booksGROUP BY category;

JOIN Types

CROSS JOINNATURAL JOININNER

Equality-joins Non-equality-joins Self-joins

OUTER: FULL/LEFT/RIGHTBoth the latter two need to use ON or

USING to specify joining conditions

Subqueries

Used in WHERE or HAVING clausesSingle-value subqueriesMultiple-value subqueries