Download 4a-SQL-Select

CSCI N207 Data Analysis with Spreadsheets
4a. Structured Query Language
- SELECT Statement
Lingma Acheson
Department of Computer and Information Science
IUPUI
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WPC Database
• What information do we need to retrieve
from the database in order to complete
some administrative tasks, or help making
business decisions?
– Who are the employees from the Production
department?
– How many employees are there in the
company?
– Can you give me the contact info for Heather
Jones?
– Who is working on project 1300?
– …?
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Structured Query Language
• Structured Query Language (SQL):
– used to query and modify database data
• Using SQL
– Show partial information
– Connect related information from different
tables
– Perform some computation
– Process information more efficiently
• SQL is a language used to send command
to a database. Must follow some grammar
rules.
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SELECT statement
• Used to display some data retrieved from
the database
• Basic frame
SELECT ColumnName(s)
FROM TABLENAME;
- Meaning: “Display this (or these) column(s)
from that table (all the rows will show).”
• The letters in red are keywords (reserved for the
database to use). They are case-insensitive.
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SELECT statement
• Select certain columns (and all rows)
Example 1, Email list of all employees:
SELECT FirstName, LastName, Email
FROM EMPLOYEE;
Example 2, All projects’ start date and end date,
SELECT ProjectName, StartDate, EndDate
FROM PROJECT;
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SELECT statement
• Save a query and give it a meaningful
name if the query needs to be executed
repeatedly. E.g. AllEmployeeEmail
• A query can be viewed just like a table,
but it’s just a real time snapshot of the
table data.
• Any update to the table will be reflected
in the query.
• Queries are also called views in some
database systems.
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SELECT statement
• Select all columns (and all rows)
SELECT *
FROM EMPLOYEE;
(query necessary?)
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SELECT statement
• Select only unique values
Example 1, show all the project start dates,
remove all the duplicate values
SELECT DISTINCT startDate
FROM PROJECT;
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