SQL Select and Relational Algebra
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SQL Select and Relational Algebra
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SQL Select and Relational Algebra. SELECT. SELECT fields FROM tables WHERE conditions GROUP BY fields HAVING conditions ORDER BY fields. SELECT * FROM expeople. SELECT name (Projection) FROM expeople. SELECT name, age FROM expeople. - PowerPoint PPT Presentation
Transcript of SQL Select and Relational Algebra
SQL Select and Relational Algebra
SELECT
SELECT fields
FROM tables
WHERE conditions
GROUP BY fields
HAVING conditions
ORDER BY fields
SELECT *
FROM expeople
SELECT name (Projection)
FROM expeople
SELECT name, age
FROM expeople
SELECT DISTINCT name
FROM expeople
SELECT sex AS gender (renaming)
FROM expeople
SELECT *
FROM expeople
WHERE age = 17 (selection)
= Equal
<> Not Equal
> Greater Than
< Less Than
>= Greater Than or Equal
<= Less Than or Equal
IS NULL
IS NOT NULL
LIKE
NOT LIKE
%
_
New% will match Newark, New York, etc.
_ow will match Cow, Bow, Now, etc.
AND
OR
SELECT *
FROM expeople
WHERE age = 17 OR name = ‘JoJo’
SELECT *
FROM expeople
ORDER BY expeople.id desc
(or can use asc)
SELECT sum(nums)
FROM exnum
count() Total number of items
sum() Sum of the items
avg() Average of the items
min() Smallest of the items
max() Biggest of the items
SELECT name, sum(number)
FROM exnum
GROUP BY name
SELECT sum(number)
FROM exnum
GROUP BY name
HAVING sum(nums) > 30
SELECT expeople.*, exjobs.*
FROM expeople, exjobs
(cartesian product)
SELECT expeople.*, exjobs.*
FROM expeople, exjobs
WHERE expeople.id = exjobs.jid(equi-joins)
SELECT *
FROM expeople
WHERE name = ‘JoJo’
UNION (union)
SELECT *
FROM expeople
WHERE age = ‘17’
SELECT *
FROM expeople
WHERE name = ‘Mike’
INTERSECT(intersection)
SELECT *
FROM expeople
WHERE age = ‘17’
SELECT *
FROM expeople
WHERE name = ‘Mike’
MINUS (set-difference)
SELECT *
FROM expeople
WHERE age = ‘17’
DONE
