1. IST 318 – DB Administration Data Retrieval Using SELECT statements

2. Data Modeling Entity: something exists and can be described Attribute: 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

3. 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

4. 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

5. SELECT Statement : basic structure SELECT – specifying what to display FROM – specifying where data come from WHERE – specifying criteria for individual records GROUP BY – specifying how to divide records into groups Having – specifying criteria for groups ORDER BY – specifying the way to sort results

6. SELECT Clause May include columns or expressions Expressions 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

7. 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)

8. WHERE Clause Logical operators may be used to build composite conditions  AND, OR, NOT Relational operators: =, <>/!=/^=, >, <,... IN (..,..) BETWEEN... AND... IS NULL/IS NOT NULL LIKE

9. 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 here Will be carried out after criteria in the WHERE clause are applied

10. HAVING Clause May only use expressions with group functions May appear before or after the GROUP BY clause

11. 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

12. 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%’

13. Single-Row Functions : for char substr(col, start, length)  substr(col, -start, length): starting from the end trim() length() ltrim/rtrim lpad/rpad(col, length, c)

14. Single-Row Functions : for number trunc(col, p)  p > 0  p = 0  p < 0 round(col, p)

15. 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

16. 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;

17. 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_SALARY FROM employees;

18. Nested Group Function 2-level tops Group by clause has to be used No other expressions without nested group functions allowed to show in the same SELECT clause  SELECT max(avg(retail)) FROM books GROUP BY category;

19. JOIN Types CROSS JOIN NATURAL JOIN INNER  Equality-joins  Non-equality-joins  Self-joins OUTER: FULL/LEFT/RIGHT Both the latter two need to use ON or USING to specify joining conditions

20. Subqueries Used in WHERE or HAVING clauses Single-value subqueries Multiple-value subqueries