queries that select records

Creating Queries in Design View− Select the fields you want to include in query.. Summarizing Data Create a totals query: − Create a new query by choosing Create ➝ Queries Query Design.

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

Understanding the SQL View

 Every query has common ingredients (thành

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

Field Name : Expression

Field Name Expression

Simple Math with Numeric Fields

 Simple Math with Numeric Fields

Operator Name Example Result

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

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

 Format(): mathematical function that

transforms numbers into text

Formatting Numbers

Currency Displays a number with two decimal places, thousand separators, and the currency sign $1,433.20Fixed 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

 More Mathematical Functions (Page 230)

 Text Functions (Page 232)

 Date Functions (Page 234)

Summarizing Data

 Total function is used to group the records to

arrive at totals and subtotals That way, you can review large quantities of information much more easily.

 Example:

− Counting all the students in each class.

− Counting the number of orders placed by each customer.

− Totaling the amount of money spent on a single product.

Summarizing Data

 Create a totals query:

− Create a new query by choosing Create ➝

Queries Query Design.➝

− Add the tables you want to use from the Show Table dialog box, and then click Close.

− Add the fields you want to use.

− Choose Query Tools Design  Show/Hide

Totals.

Summarizing Data

 For each field, choose an option from the Total

box This option determines whether the field is used in a calculation or used for grouping.

 Every field must belong to one of these

categories:

− It’s used in a summary calculation (like

averaging, counting, …)

− It’s used for grouping.

− It’s used for filtering

Summarizing Data

Choice in the

Total box Description

Group By Subgroups records based on the values in this field.Sum Adds together the values in this field.

Avg Averages the values in this field.

Min Retains the smallest value in this field.

Max Retains the largest value in this field.

Count Counts the number of records (no matter which field you use).First Retains the first value in this field.

Last Retains the last value in this field.

Summarizing Data

 Example: Calculate Total for every Order

Query Parameters

 Query parameters let you create flexible queries

by enter one pieces of information

 Every time you run the query, Access prompts

you to supply the missing values These missing values are the query parameters.

 Usually, query parameters are used in filter

conditions

 When run the query, you fill in the value you

want to use at that particular moment.

Query Parameters

 To create a query that uses parameters:

− Create a new query by choosing Create  Queries 

− Choose a name and data type for parameter.

− Click OK to close the Query Parameters dialog box.

Crosstab Queries

 A crosstab query is a powerful summary tool that

examines huge amounts of data and uses it to

calculate information like subtotals and

averages.

 Crosstab queries use two key ingredients:

grouping and summary functions

− The grouping is used to organize the rows into small sets

− The summary function is used to calculate a

single piece of information for each group.

Crosstab Queries

 Creating Crosstab Queries: have two ways to

create a crosstab query:

− The Crosstab Query Wizard provides an

automated way to create a Crosstab query The wizard works only with one table or query.

− Build Crosstab Query by hand.

Crosstab Queries

 Creating a Crosstab Query with the Wizard

− Display the Create tab on the Ribbon.

− Click the Query Wizard button in the Macros &

Code group on the Ribbon.

− The New Query dialog box opens.

− Select the Crosstab Query Wizard option and then click OK.

− Select the table or query that contains all the fields you need for your Crosstab query, and then click Next.

Crosstab Queries

− Select the field(s) whose values you want to use

as row headings  click Next.

− Select the field(s) whose values you want to use

as column headings  click Next.

− If select a date field as the column headings,

Choose how to group dates from the list Next.

− Choose the field whose values grouped by the row and column headings that are selected.

Crosstab Queries

− Select a grouping method from the Functions list.

− Choose whether to include row sums by

selecting the check box on the same page as the function choices, and then click Next.

− Name the query and then click Finish to see the Crosstab query.

Crosstab Queries

 Creating a Crosstab query in Design view: A

simple Crosstab query has three fields:

− One used for row headings

− One used for column headings.

− The Value field, which contains the data that you want to appear in the cells of the table Tell Access how to summarize your data in the

Crosstab query by choosing from these choices: Sum, Avg, Min, Max, Count, StDev, Var, First, or Last.

Crosstab Queries

− Choose Create Queries Query Design.➝ ➝

− Add the table or query you want to use in

crosstab query.

− Query Tools  Design Query Type  Crosstab.

− Choose the fields use for row labels and in the Crosstab row, choose the Row Heading.

− Choose the fields use for Column labels and in the Crosstab row, choose the Column Heading.

Crosstab Queries

− Select the field containing the values that you want aggregated, in the Crosstab row, choose the Value option.

− Set the Total row:

 Group By option for column heading and row

heading

 Choose summarize the data for the Value

field column.

Crosstab Queries

 Example: