A quick guide, 50,00 feet on SQL

1. Quick Intro SQL
it’s SEA QUELL

2. What is SQL
SQL stands for
Structured
Query
Language
● It is used to access, manipulate and
process data in databases.

3. What is a database?
A database is a place that stores data, derived
information and process logic.
Common Forms:
● RDBMS - Relational Database Management
System
● NoSQL - a grab bag of multiple systems to
store data

4. Parts of a RDBMS
● Database / Catalog
● Schema
● Table/ Indices
● View
● Row / Record
● Field / Column
● Stored Procedures/ Functions

5. Column / Field
A column (or field) is a single piece of data, that
has a defined type and a set purpose
● Text
● Number
● more complex types depend on the RDBMS

6. Record / Row
A record is a collection of fields grouped
together to provide context to the data
contained

7. Table / Indices
A table is a collection of records which set
operations can be applied to

8. So what?
Why is this useful, a database provides a means
to represent real world models and hence
understand through analysis more about the
system modelled

9. Data Modelling 101
What to model?
● Groceries
● Contact list
● Calendar
You choose :)

10. What were those join-ey
things
● They can relate tables to each other
● Provide links to information for context
● Minimize storage

11. Database Forms
First Normal Form
● Eliminate repeating groups in individual
tables.
● Create a separate table for each set of related
data.
● Identify each set of related data with a
primary key.

12. Database Forms
Second Normal Form
● Create separate tables for sets of values that
apply to multiple records.
● Relate these tables with a foreign key.

13. Database Forms
Third Normal Form
● Eliminate fields that do not depend on the
key

14. So how do I get data?
SELECT statment
● Allows you to SELECT data FROM several
tables WHERE certain constraints exist, and
GROUP BY certain fields, it can be ORDER
BY other fields

15. SELECT
SELECT
employeeName,
startDate,
FROM
employees
WHERE startDate => GETDATE()-7

16. JOINS
There are various join types in SQL
INNER
LEFT OUTER
LEFT OUTER …. ON t2.field IS NULL
FULL OUTER

17. Joins...
SELECT …
FROM employee e
INNER JOIN jobtitle j
ON e.jobId = j.jobId

18. Nested Tables
SELECT …
FROM (
SELECT …
FROM employee
) subTable

19. More Complexity...
Depending on the platform we have function
that can help process, manipulate and pivot
data

20. CASE statements
CASE
WHEN x
THEN y
ELSE z
END AS simpleCase

21. Common Table Expressions...
WITH tableDef(fieldlist)
AS (
… complex query
)
SELECT ….

22. Recursive CTE...
WITH empTree AS (
SELECT …, 0 AS level
FROM employee
UNION ALL
SELECT …, level + 1 AS level
FROM employee INNER JOIN empTree ON ...

23. PIVOT and UNPIVOT
SELECT 'AverageCost' AS Cost_Sorted_By_Production_Days,
[0], [1], [2], [3], [4]
FROM
(SELECT DaysToManufacture, StandardCost
FROM Production.Product) AS SourceTable
PIVOT
(
AVG(StandardCost)
FOR DaysToManufacture IN ([0], [1], [2], [3], [4])
) AS PivotTable;

24. LAG
SELECT BusinessEntityID,
YEAR(QuotaDate) AS SalesYear,
SalesQuota AS CurrentQuota,
LAG(SalesQuota, 1,0)
OVER (ORDER BY YEAR(QuotaDate)) AS PreviousQuota
FROM Sales.SalesPersonQuotaHistory
WHERE BusinessEntityID = 275 and YEAR(QuotaDate) IN
('2005','2006');

25. Designing complex SQL
Diagram the flow
Model the output
Doodle :)