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Review quiz. Answer questions.
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Discuss queries:
◦ What is a query? Turning data stored in a database into
information for decision making.
◦ You: Completed two tutorials with step-by-step instructions for
creating queries in MS Access. Now must apply knowledge and
skills learned in the tutorials.
◦ Class today:
 Highlight key issues about queries.
 Explain aspects of MS Access queries in more detail.
 Answer any questions about queries in preparation for
completion of the next part of the project (due 10/04).
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What is the difference between a query
and a table?
What is the difference between a query
datasheet and a table datasheet?
Why do we create queries when we
already have data in tables?
Result
Table
Query
Underlying Tables
A query reduces the number of
rows and columns in the
underlying tables to provide
information for decision making.
A query enhances the data in the
underlying tables by adding
calculations and logical
conditions.
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Table contains structure of data, constraints and
actual data.
◦ Table is referred to as “underlying data”.
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Query is a way to look at the data.
◦ Queries seldom look at the complete contents of a table because
tables are usually very big, with many columns and many rows.
◦ The goal of creating a query is to provide appropriate data for
decision making.
◦ Queries “filter” the data; fewer columns, fewer rows, calculated
fields, summarized information.
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Individual row queries.
◦ Using one table.
◦ Using multiple tables.
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Aggregate queries.
◦ Creating one line in the result table.
◦ Creating multiple groups in the result table.
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Parameter queries.
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Pre-written functions exist to do common
summary calculations:
◦ Sum, count
◦ Max, min
◦ Avg, stDev, var
◦ First, last
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Can do calculations for all data in a result table,
or grouped data in a result table
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Criteria.
◦ And vs. Or
◦ Relational operators. <, >, =, IN, LIKE
◦ Wildcards
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Multiple tables.
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Calculations.
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Logical conditions.
◦ IIF
◦ NOT
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Each value in a field has very specific data coded for a
computer to read.
Humans can discern vague similarities and differences
among data fairly easily. Computers are more exacting.
Computers need you to tell them when data is a date, or
a character, or a number.
A zero is not the same as a blank which is not the same
as a null.
A null is a special character assigned to a field that
technically has “no value”. It is very useful because we
can search for a null value with special operators.
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Computers require very explicit instructions.
MS Access has default instructions, but that is because
it is considered a very friendly, user-oriented package.
Normally, must be very explicit about relational
operators on the conditions of queries.
◦ =, >, <, >=, <=
◦ Like
◦ Between
◦ In
◦ Is
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Wildcard is an asterisk.
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Referred to as “joining” tables.
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Can produce confusing results.
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Very dependent on a well-designed database. The
tables must be related with appropriate foreign
keys or the tables cannot be joined correctly for
queries.
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Frequently want to see if something is TRUE or
FALSE.
Example: If a training event has > $500 in
expenses, then it is a high expense event.
Logical condition for Access:
◦ IIF(trainingexpenses + travelexpenses > 500, “high expense”)
◦ IIF(ISNULL(trainingexpenses + travelexpenses), 0)
◦ IIF(ISNULL(trainingexpenses + travelexpenses), 0,
trainingexpenses + travelexpenses)
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5 minutes.
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Turn to the person or people next to you.
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Describe at least 3 queries that would be relevant
to the training database we use for the Access
project.
◦ None of the queries can be from the Access Project Part 2.
◦ Make sure that one of the queries requires calculations.
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Design view: Used to structure a query. Referred to as
“query by example” or QBE.
Result table: The table produced by the query. Shown
in the datasheet view.
SELECT query window: The window displayed in design
view that is filled out to produce a result table. Also
called the query design grid.
Field row: The area in the SELECT query window used to
define what columns should appear in the result table.
Criteria row: The area in the SELECT query window used
to identify which rows should appear in the result table.
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Can do calculations for a column based on the data
in other columns for that same row.
Can use mathematical operators.
Can use pre-written functions in MS Access. Many
different types of pre-written functions for date
handling, data type conversion, calculations, etc.
◦ See the pre-written functions in the expression builder.
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Can be very simple to very complicated.