queries that select records

Queries That Select Records
(Chapter 6 – 7)
Query Basics

A Microsoft Access query is a question about the
information stored in Access tables.

Your query can be a simple question about data
in a single table, or it can be a more complex
question about information stored in several
tables.

After run query, Microsoft Access returns only
the information you requested.
Creating Queries in Design View

The best starting point for query creation is the
Design view.
−
Choose Create  Queries  Query Design.
−
Select the table that has the data you want,
and then click Add  Click Close.
Creating Queries in Design View
−
Select the fields you want to include in query.
−
Arrange the fields from left to right in the order
to appear in the query results.
−
If you want to hide one or more columns, then

clear the Show checkbox for those columns.
Creating Queries in Design View
−
Choose a sort order.
−
Set your filtering criteria by place the expression into the
Criteria box for the appropriate field.
−
Choose Query Tools Design  Results  Run. Save
the query.
Getting the top records

Use the Top Values box on the Design View
toolbar to see the top records produced by the
query.
−
Open query in Design view.
−
Sort table so that the records you’re most
interested in are at the top.
−
In the Query Tools  Design
−
Query Setup  In return box,
−
 choose a different option
Creating Queries by Wizard

Create a simple Query by using wizard.


The Query wizard works by asking you a series of
questions.
−
Choose Create  Queries  Query Wizard.
Creating Queries by Wizard
−
Choose a query type. The Query wizard includes a
few common kinds of queries.

Simple Query Wizard.

Crosstab Query Wizard.

Find Duplicates Query Wizard.

Find Unmatched Query Wizard
−
OK.
−
In the Tables/Queries box, choose the table that has
the data you want.
Creating Queries by Wizard
−
Add the fields you want to see in thequery
results
−
Click Next. Enter query name  Click Finish.
Understanding the SQL View

Behind the scenes, every query is actually a text

command written in a specialized language called
SQL (Structured Query Language).

To take a look at the SQL command for a query,
right-click the tab title, and then choose SQL view.

Example:
1 SELECT Products.ID, Products.ProductName, Products.Price
2 FROM Products
3 WHERE (((Products.Price)>50))
4 ORDER BY Products.Price;
Understanding the SQL View

Every query has common ingredients (thành
phần), represented by:
−
SELECT: list of fields appear in the query
results.
−
FROM: indicates the table (or tables) that
you’re searching.
−
WHERE: indicates the start of your filter
conditions.
−
ORDER BY: define the sorting order.
Queries and Related Tables

A join line connects tables in the query design.
The join line connects the primary key in one

table to the foreign key in another table.

By default, an Access query returns only records
where data exists on both sides of a relationship.

To see records that are not matched on the other
side of the join. You must modify the default
query join.
Queries and Related Tables

Can create joins between tables in these three
ways:
−
By creating relationships between the tables
when you design the database.
−
By selecting two tables for the query that have
a field in common that has the same name
−
By modifying the default join behavior
Queries and Related Tables
Calculated Fields

To create a calculated field, you need to supply
two details:

Example: define the PriceWithTax calculated
field:
PriceWithTax: [Price] * 1.10
Field Name : Expression

Field Name
Expression
Simple Math with Numeric Fields

Simple Math with Numeric Fields
Operator Name Example Result
+ Addition 1+1 2
– Subtraction 1–1 0
* Multiplication 2*2 4
^ Exponentiation 2^3 8
/ Division 5/2 2.5
\ Integer division 5\2 2
Mod Modulus 5 Mod 2 1
Expressions with Text

To join text, use the ampersand (&) operator.

For example:
−
Create a FullName field from the FirstName
and LastName fields:
FullName: [FirstName] & “ “ & [LastName]
−
To “The price is” to appear before each price
value, use this calculated field:
Price: "The price is: " & [Price]
Query Functions

A function is a built-in algorithm that takes some
data that you supply, performs a calculation, and

then returns a result.

Functions is used in:
−
Calculated fields. To add information to your
query results.
−
Filter conditions. To determine what records
you see in a query.
−
Visual Basic code.
Using a Function

To use a function:
−
Enter the function name, followed by
parentheses.
−
Inside the parentheses, put all the information
the function needs in order to perform its
calculations.
Example:
SalePrice: Round([Price] * 0.95, 2)
The Expression Builder

To quickly find the functions you want, Access
provides a tool called the Expression Builder.

To launch the Expression Builder:
−

Open a query in Design view.
−
Right-click the box where you want to insert
your expression, and then choose Build.
−
Add or edit the expression.
−
Click OK.
The Expression Builder

To find a function:
−
Expand the Functions item, and choose Built-In
Functions.
−
Next, choose a function category in the
Expression Categories list.
−
The Expression Values list will show all the
functions in that category.
−
Double click on functions name to insert it into
your expression.
Formatting Numbers
Formatting Numbers

Format(): mathematical function that
transforms numbers into text.

Example:

SalePrice: [Price] * 0.95
−
Use the Format() function to apply a currency
format:
SalePrice: Format([Price] / 0.95, "Currency")
Formatting Numbers
Format Description Example
Currency
Displays a number with two decimal places,
thousand separators, and the currency sign.
$1,433.20
Fixed
Displays a number with two decimal places.
1433.20
Standard
Displays a number with two decimal places
and the thousands separator.
1,433.20
Percent
Displays a percent value. Displays 2 digits to
the right of the decimal place.
143320.00%
Scientific
Displays a number in scientific notation, with
two decimal places.
1.43E+03
Yes/No
Displays No if the number is 0 and Yes if the
number is anything else.
Yes

Functions

More Mathematical Functions (Page 230)

Text Functions (Page 232)

Date Functions (Page 234)