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4a. Structured Query Language- SELECT Statement

Lingma AchesonDepartment of Computer and Information Science

IUPUI

CSCI N207 Data Analysis with Spreadsheets

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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, EmailFROM EMPLOYEE;Example 2, All projects’ start date and end date,SELECT ProjectName, StartDate, EndDateFROM 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 valuesExample 1, show all the project start dates, remove all the duplicate valuesSELECT DISTINCT startDateFROM PROJECT;