Download RDBMS and SQL

RDBMS and SQL
• RDBMS = Relational Database Management System
• SQL = “Structured Query Language”
– Programming Language to Interact with an RDBMS
– Pronounced as “sequel”
2/23/16
CprE/SE 419, Srikanta Tirthapura
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RDBMS
• An RDBMS consists of data viewed as one or more tables
• Each table can be viewed as many “rows”
• Each table can be viewed as many “columns”
• Each row consists of values assigned to each of many attributes
• Table stores a mathematical Relation
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CprE/SE 419, Srikanta Tirthapura
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RDBMS Schema
• A specification of the set of tables in the database.
• For each table, a specification of the types and names of each column in the table
All rows in a table have the same schema
(Compare the above with Pig)
Vocabulary: Table, Row, Column, Schema
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CprE/SE 419, Srikanta Tirthapura
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Example
Consider the following Tables
1. Sailors (sid: integer, sname: string, rating: integer, age: real)
2. Boats (bid: integer, bname: string, color: string)
3. Reservations (sid: integer, bid: integer, day: dates)
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CprE/SE 419, Srikanta Tirthapura
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SQL
• Data Definition Language (DDL)
– Define the database structure and schema
– Create, Alter, Drop, etc
• Data Manipulation Language (DML)
– Query and update data
– SELECT
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CprE/SE 419, Srikanta Tirthapura
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A basic query in SQL
SELECT select-­‐list
FROM from-­‐list
WHERE qualification
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CprE/SE 419, Srikanta Tirthapura
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SQL Clauses
• FROM clause: the from-­‐list is a list of table names
• SELECT clause: the select-­‐list is a list of (expressions involving) column names of tables
• WHERE clause: qualification is a predicate involving columns of the tables
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Example 1
Find the names and ages of all sailors.
SELECT sname, age
FROM Sailors
or
SELECT S.sname, S.age
FROM Sailors S
Note that a SQL table is a set, not an ordered list, so names will not be printed in any particular order
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CprE/SE 419, Srikanta Tirthapura
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Example 2
Print out information about all sailors younger than 25 years
SELECT sid, sname, rating, age
FROM Sailors
WHERE age < 25
equivalently written as
SELECT * FROM Sailors
WHERE age < 25
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CprE/SE 419, Srikanta Tirthapura
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Example 3
Find the names and ids of sailors who have reserved boat id 103
SELECT S.sname,
FROM Sailors S, Reservations R
WHERE S.sid = R.sid AND R.bid = 103 equivalently,
SELECT Sailors.sname, Sailors.sid
FROM Sailors, Reservations
WHERE Sailors.sid = Reservations.sid AND Reservations.bid = 103 2/22/16
CprE/SE 419, Srikanta Tirthapura
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Example 4
Find the names of all sailors who have reserved at least one boat.
SELECT S.sname
FROM Sailors S, Reservations R
WHERE S.sid = R.sid
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CprE/SE 419, Srikanta Tirthapura
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Example 5
Find the names of all sailors who have reserved a red boat
SELECT S.sname
FROM Sailors S, Boats B, Reservations R
WHERE (S.sid = R.sid) AND (R.bid = B.bid)
AND (B.color = ‘red’) 2/22/16
CprE/SE 419, Srikanta Tirthapura
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Example 6
Find sids of all sailors who have a rating of 10 or have reserved boat 111
SELECT S.sid
FROM Sailors S
WHERE S.rating = 10
UNION
SELECT R.sid
FROM Reservations R
WHERE R.bid = 111
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CprE/SE 419, Srikanta Tirthapura
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Example 7
Find the average age of sailors
SELECT AVG (age)
FROM Sailors
Find the average age of sailors with a rating of 10
SELECT AVG (age)
FROM Sailors WHERE rating = 10
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CprE/SE 419, Srikanta Tirthapura
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Example 8
Find the name of the sailors with the maximum age
SELECT S.sname, S.age
FROM Sailors S
WHERE S.age = (SELECT MAX (S2.age)
FROM Sailors S2)
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CprE/SE 419, Srikanta Tirthapura
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Example 9
Find the names of sailors who are older than the oldest sailor with a rating of 10
SELECT S.sname
FROM Sailors S
WHERE S.age > (SELECT MAX(S2.age)
FROM Sailors S2
WHERE S2.rating = 10)
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CprE/SE 419, Srikanta Tirthapura
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Example 10
Find the number of reservations for each sailor
SELECT S.sid, COUNT(*)
FROM Reservations
GROUPBY S.sid
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CprE/SE 419, Srikanta Tirthapura
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Data and Metadata
• Data: – Actual contents of tables
– Ex: Sailors, Boats, Reservations
– Stored on HDFS
• Metadata:
– Table Schemas
– Stored in a metastore
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