access 2010 - select queries

8/11/2019 Access 2010 - Select Queries

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Access 2010

Select Queries


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Select Queries

Table of ContentsIntroduction .................................................................................................................................................. 1

Retrieving Data from Tables ......................................................................................................................... 1

Query Design View .................................................................................................................................... 1

Query Results View ................................................................................................................................... 3

Add Criteria to a Query ............................................................................................................................. 5

Query Criteria ........................................................................................................................................ 5

Comparison Operators .......................................................................................................................... 6

Conditional Operators ........................................................................................................................... 6

Add a Calculated Field to a Query ............................................................................................................. 8

Operators .............................................................................................................................................. 8

Expressions ............................................................................................................................................ 8

Performing a Calculation on a Group of Records ................................................................................... 10

Creating Flexible Queries ............................................................................................................................ 12

Setting Top and Bottom Values .............................................................................................................. 12

Showing Records Containing Unique Values .......................................................................................... 12

Creating Parameter Queries ................................................................................................................... 14

The LikeOperator and Wildcards ....................................................................................................... 14

The BetweenAndOperator ............................................................................................................... 15

TheAmpersand (&) ............................................................................................................................. 15

The Prompt Message .......................................................................................................................... 15


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Introduction

When designing a database, first the data model is created and tables and relationships are defined in

Access. Next, test data is entered, the design is further refined and field properties are used to ensure

consistency when entering and updating data. Then, filters can be created and applied in each tables

datasheet view to display subsets of the information stored in that table. In this topic, we are now

ready to use select queries to retrieve data from one or more tables in order to answer questions about

the data.

Although there are many different types of queries that can be created and used in Access, this topic will

be covering select queries. We will begin by creating select queries to retrieve data from multiple

tables. We will then move on to summarizing data in queries. Finally, we will create new calculated,

query fields based upon data stored in the tables.

Retrieving Data from TablesFiltering allows you to display all of the fields for selected data from a single table and to save the filter

with the table. However, you may need to display only certain fields for selected data from multiple

tables. Select queries allow you to retrieve relevant information from different tables at the same time.

You can also save query designs as named, reusable Access objects.

Query Design View

Tables can be very large; containing many fields and records. Select queries enable you to choose onlythe fields that are relevant and retrieve only the records necessary for the task you are trying to

accomplish. In the Query Design view window, table field lists are displayed in the upper pane and the

selected fields and desired attributes are displayed in the query-by-example grid in the lower pane.


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The Query Design window is opened by clicking the Query Design button found on the Create tab in the

Other group.

Once opened the Query Design window displays the Show Table dialog box. To add tables to the upper

pane of the query design window, select the desired table(s) and click Add. Tables can be added one-by-

one or all at once by holding the Ctrl key when selecting them. Once tables have been added, the Show

Table dialog box must be closed by clicking the Close button. The Query Tools Design contextual ribbon

tab displays indicating that a Select query is the default Query Type and that Table Names are displayed

by default in the query grid. Note: Once closed, the Show Table dialog box can be redisplayed by

clicking the Show Table button in the Query Setup group.

If relationships between the selected tables were previously defined in the relationships window a join

line connecting the tables will automatically display. If referential integrity was enforced when the

relationship was created, the join line will show the relationship type, i.e. One-to-Many or One-to One.

If no relationships between the tables were previously defined, a join line will not display automatically

and the tables will need to be joined by dragging a join line between the related fields.


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Query Results View

Query results can be viewed by

clicking the View or Run button

located in the Results group on

the left side of the Query Tools

Design contextual tab.

Query results display in

datasheet view and the Query

Tools Design contextual tab

closes. To redisplay the query

design view, click the View

button on the left side of the

Home tab.

The query design can be saved

by clicking the Save button on

the Quick Access toolbar and

assigning a name to the query.

Note: Queries can be saved in

either the design view or the

results view but it is the designof the query that is saved, not

the results it produces at that

time.

Once saved, the query is then available by

selecting it from the Queries group in the

Object Navigation bar.


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Add Criteria to a Query

In addition to selecting certain fields to be displayed, queries can also be used to select a subset of data

in a single table or across multiple tables that satisfy specific criteria and can be sorted in different ways.

Query Criteria

Query Criteriaare the search conditions used in a query to retrieve or manipulate specific information.Multiple criteria as well as sort selections can be included in a query. The query criteria are used to

compare the information in the fields to specific values and retrieve the records that meet the

condition(s). The order of the information retrieved can be changed using the Sort features in the query

grid. Sortselections are: ascending, descending and not sorted. Sort precedence is from left to right

within the query grid. Display of one or more fields in the results can be controlled by using the Show

checkbox for the field(s). Selected fields are displayed by default (checked). Display can be suppressed

by removing the check from the Show checkbox.

Note: It is recommended that the results be reviewed, using the View button, each time criteria is

added or changed in the query design. This will determine if the desired results are being displayed at

each step in the data retrieval process. If the results at any step are not what were expected, then theprevious criteria entered or changed is likely the reason and can be adjusted accordingly. This can save

valuable time in determining what went wrong, where and when in the event that a querys results

are not what were expected.


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Comparison Operators

Comparison Operatorsare symbols used to compare two values. Comparison operators, when set in

criteria, establish results after comparing two or more values. The output of a comparison is either true

or false.

Operator Value Example

= Equals =NJ

< Less Than = Greater Than or Equal To >=1/1/2011

Not Equal To NY

BetweenAnd Within a Range Between 100 And 500

Is Null Null Values Is Null

Conditional Operators

Conditional Operatorsare operators that test for the truth of a condition. Conditional operators, as with

comparison operators, return a value of either true or false. Parentheses can be used to change theorder of evaluation, and the operators within parentheses are evaluated first. Conditional operators are

also commonly referred to as logical operators.

Operator Description Example

AND True if both conditions are true. >5 AND


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Additional Information regarding Query Criteria

The Access query grid provides multiple rows in which you can specify the records that need to be

retrieved in the result set. For example, if you wanted to select all of the records where a Price field is

greater than $100, you would type >100 in the criteria row below the Price field in the query grid. Using

ANDs and Ors allows you to expand or narrow the search. If you wanted to select all of the records

where the Price field is greater than $100 AND where the location of the sale is the State of California,

you would add the word California to the criteria row below the State field. When both criteria are

placed on the same line, an AND condition is automatically created. An AND condition narrows the

search because the records that are selected must meet all of the criteria in order to be retrieved.

Putting criteria on a different line creates an OR condition, which expands the search. Using the

previous example, if the word California below the Statefield was moved down one row to the OR

row of the query grid, the query would retrieve all records where the Price field is greater than $100

(from any state) as well as all records where the State field is equal to California (regardless of the price).

AND and OR conditions may also be typed directly into the same cell in the query grid. For example, you

could type California OR Michigan in a State fields criteria row to return all records from either

state. Typing California AND Michigan in the State fields criteria row would not return any records

because the value in the State field, for a single record, cannot be equal to both California and Michigan

at the same time.

Field display, as well as sort precedence, in the results view can be controlled by adding criteria to a field

in the query grid and not showing it in the results view or by adding a field to the query grid a second

time, for sorting purposes, but not showing it in the results view.

Procedure Reference: Add Criteria to a Query

1.

Create a new Select Query or open the desired Select Query in Design view.2.

In the query grid include the field or fields for which you wish to set criteria.

3.

Set the criteria.

To create an AND or OR condition on a single field, include the appropriate word in the

Criteria row for that field.

To create an AND condition on more than one field, enter the additional criteria in the

Criteria row for the additional field(s).

To create an OR condition on more than one field, enter the additional criteria in the OR

row for the additional field(s).


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Procedure Reference: Performing Calculations on a Group of Records

1. Open the desired query and switch to Design view or create a new query in Design view.

2. Click the Totals button in the Show/Hide group, on the Design contextual tab.

3.

Add the fields to the design grid on which you wish to group the records.4. Add the fields to the design grid that you wish to calculate using aggregate function(s).

5.

For each field, from the Group By drop-down list, select Group Byor the desired aggregate

function.

6. If desired, enter selection criteria in the Criteria row(s). Note: If selection criteria must be

entered for a field which is not to be grouped, include that field in the design grid and from the

Group By drop-down list, select Where.

7. If desired, select sort order(s) from the Sort row.

8.

Save the query, assigning a name if necessary.

9. View or run the query to display the results.

Note: When grouping records and using aggregate functions, newly created calculated fields cannot be

used in other calculations within the same query. To resolve the error message either re-create the

additional calculated field(s) without the newly created field or create a new query based upon the

previous query to perform the grouping and aggregate functions.


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Creating Flexible QueriesWeve seen that creating and using queries allows for quick access to all kinds of information in a

database. Surprisingly, select queries can be even more flexible in their functionality. You can use

them to display specific subsets of data by showing Top, Bottom or Unique values. Also, using

Parameter prompts, you can be prompted to enter different criteria each time the query is run, rather

than entering specific criteria in the query grid.

Setting Top and Bottom Values

Displaying the top or bottom values in a query results list involves two steps. First the query results

must be sorted, either ascending (for top values) or descending (for bottom values), on the desired field.

Then, the number or percent of the top or bottom values must be set using the Return option in the

Query Setup group of the Query Tools Design contextual tab or the Top Values property on the Query

Properties sheet. Note: Entry is not restricted to the items listed. Numeric or percentage values may

be typed into the Return combo box or the Top Values property.

Showing Records Containing Unique Values

The Query Propertiessheet contains other items, in addition to the Top

Values property, that affect the entire query. The Unique Valuesproperty

can be used to restrict the records returned to those that have unique field

values in the query design grid. Similarly, the Unique Recordsproperty can

be used to restrict the records returned to those that have unique values inall fields in the underlying tables or queries.

The Query Properties sheet can be opened by right-clicking a blank area of

the upper pane of the query design window and selecting Propertiesfrom

the short-cut menu or by clicking the Property Sheet button in the

Show/Hide group of the Design contextual tab.


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Procedure Reference: Setting Top or Bottom Values

1.

Open the query in design view.

2. For the desired field in the Design grid, in the Sort cell, select either Ascending or Descending.

3. View or run the query to observe the results.

4. Return to Query Design view.

5.

Set the numeric or percentage value for the subset of records desired.

On the Design contextual tab, in the Query Setup Group, provide a value for the Return

property box by selecting or typing a number or percent value.

Or, in the Query Properties pane provide a value for the Top Values property field by

selecting or typing a number or percent value.

6. View or run the query to observe the results.

Procedure Reference: Showing Records Containing Unique Values

1. Open the query in design view.

2. Display the Query Properties Sheet pane.

Right-click in a blank area in the top of the query design and select Properties. Or, Click the Property Sheet button in the Show/Hide group on the Query Tools Design

contextual tab.

3. Set the Unique Values property to Yes or set the Unique Records property to Yes.

4. View or run the query and observe the results.


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Creating Parameter Queries

A Parameter Queryis a flexible query that prompts the user for additional criteria. Instead of the actual

criteria, a message or command is placed in the criteria row beneath the applicable field. The message

must be enclosed in square brackets ([ ]). When the query is run, this text appears as a prompt, awaiting

input from the user. A parameter query can prompt for more than one criterion, with a separate dialog

box displayed for each.

The LikeOperator and Wildcards

A wildcard is a special character used to include or exclude a single character or a group of characters in

a search. A wildcard is a symbol that enables you to substitute a different character in order to provide

criteria for pattern matching. Wildcards can be used in the criteria of a query as well as in a parameter

prompt. You can use the Likeoperator with one or more wildcards to display query results that match

specific values in a field that follows the pattern set by the wildcards. You can also use wildcards in

response to parameter prompts.

Common Wildcards

Character Description Example

* Matches any number of characters but can only

appear at the beginning or the end of the

string.

Like S*would match Stone, Smith

and Sullivan. Like *s would match

Lakes and Snakes.

? Matches any single alphabetical character and

can appear in the middle of a string.

Like B?nd would match Band, Bind

and Bend, among others.

[ ] Matches any single character provided within

the brackets.

Like B[ai]nd would match Band and

Bind, but not Bend or Bond.

[! ] Matches any character not provided within the

brackets.

Like B[!a]nd would match Bend,

Bind and Bond, but not Band.

[ - ] Matches any single character from within the

range provided in the brackets

Like B[a-d]nd would match Band,

Bbnd, Bcnd, and Bdnd only.

# Matches any single numeric character and can

appear in the middle of a number.

Like 9#7 would match 901, 917,

927, etc.

Brackets

Text appears as a prompt

Dialog Box


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The BetweenAndOperator

Another valid operator in a parameter query is the BetweenAndoperator. To check for a range of

values in a single cell, use the BetweenAnd operator with the bracketed prompts. For example, typing

Between [Please enter the start date:] And [Please enter the end date:] into the criteria row of a date

field would locate records that have date values that are between the start and end dates provided by

the user in response to the prompts.

TheAmpersand(&)

The ampersand is a concatenation operator that is used to join two character strings end to end. It is

usually accomplished by putting the ampersand character between the strings. It can be used along with

the asterisk (*) wildcard to link more data to criteria specified by the user as part of a parameter query.

The Prompt Message

When you specify a prompt message in a parameter query, it should be brief but meaningful. Access

can display up to 50 characters in the prompt message. Periods, exclamation marks and square

brackets are not allowed within the outer square brackets. Also, the message cannot be the same as the

field name but can include the field name.

Note: Shift+F9 can be used to re-run a query.

Procedure Reference: Create and Run a Parameter Query

1. Open a query in design view or create a new query.

2. Click in the Criteria cell for the appropriate field and type the prompt message within square

brackets ([ ]).

3. If necessary, enter Like, the concatenation operator &and the desired wildcards within the

criteria.

4.

View or run the query.

5. In the Enter Parameter Value dialog box, type appropriate data in response to the prompt.

6. Click OK.

7. Query results will display the records which match the data entered.

Wildcard

Concatenation Operator

Like Operator

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