DB Implementation:
MS Access Queries
1
Outline

Access Queries
►
►
►
►
Query Creation
Sorting & Filtering
Query Types
Dynamic Query
2
MS Access Queries

Database Queries
►
►

Core DBA skill
From SQL to Query by Example (QBE)
What does it do?
►
Find target information
• Retrieve, Filter, Sort, Aggregate/Summarize
►
Manipulate data
• Perform calculations
• Add, Change, Delete, Combine data in tables
• Assemble/Supply data for forms and reports

How does it work?
►
►
►
Access translates QBE to SQL
SQL performs data manipulations based on Relational Algebra
Access queries create a dynaset (“live” view of table)
• changes made in data by query is reflected in underlying tables
3
Access Queries: Views

Datasheet view
►
►

For displaying the result of the query
Useful for reviewing/validating the query
Design View
►
►
For creating/modifying a query using drag & drop GUI (i.e., QBE)
Consists of Diagram Pane & Grid Pane
•
•
►
Can sort/filter/compute by fields
•
•
•
►

Add tables/queries to the Diagram Pane
Add fields to the Grid Pane (Field row)
Sort row: set to Ascending/Descending
Criteria row: use Expression to apply data filter
Total row: compute (sum, min, max, count, etc.) of each field
Automatically generates SQL statements
SQL View
►
►
For creating/modifying a query by manually writing SQL statements
Only way to create SQL-specific queries
•
Union/Data-definition/Pass-through query
4
Access Queries: Basic Types

Simple Query
►
►

Uses one table/query
To generate a subset (row/column) of a table
Multi-table Query
►
►
Joins multiple tables/queries
To merge small chunks of data in normalized tables
•
•

Select Query
►
►

Linked tables are automatically linked in in the Query Design Grid
Creating a link in the Query Design Grid does not permanently link tables
Selects records that meet given criteria
Does not change the data
Parameter Query
►
Prompts for query criteria values (parameters) to run a dynamic query
5
Access Queries: Sort & Filter

Datasheet View
►
Sorting
• Click column and right-click
►
Filtering
• Filter Tool (Home tab)
 Filter by Selection
 Filter by Form
 Advanced Filter/Sort

Design View
►
Sort using the Sort Row
• Sort priority is from left to right for multiple sort
►
Filter using the Criteria Row
• Criteria in multiple rows make OR query
• Criteria in single row make AND query
• Criteria in a single cell


AND/OR
Wildcards (*) in Like and Between
–
e.g. Like “A*”, Like “[A-C]*”, Like “*av*”, Like “ave?”, Not Like “A*”
–
e.g. Between 1950 and 1960, >1960
6
Access Queries: Query Criteria

Query Criteria Expressions
Expression
Returns
Between #1/1/99# and #12/31/99#
Dates from 1/1/99 to 12/31/99
In (“John”,”Mary”,”James”)
Records with John, Mary, or James
Is Null
Records with no entry
Like “Acc?ss”
‘Acc’ followed by any character, followed by ‘ss’
Like “*s”
Ends in ‘s’
Like “v*”
Starts with ‘v’
<1000
Less than 1000
1000
Equal to 1000
Like “[A-C]??”
Starts with A through C and has two more characters
????
Any four characters
Len([Surname])= Val(4)
Any Surname of 4 characters
Right([Surname],2)= “ss”
Any Surname ending in “ss”
Left([Surname],2)= “ac”
Any Surname starting with “ac”
7
Access Queries: Expressions

Using expressions to create a calculated column
►
Enter expressions in blank column of query design view
• NAME: [Field1] operator [Field2]
►

Format the display in Format property of the field
Examples
►
Simple math
• DiscountPrice: [Discount] * [StandardPrice]
►
String Concatenation
• Name: [FirstName] & “ ” & [Lastname]
►
Date & Time math
• DateDiff(Interval, BeginDate, EndDate)

HireAge: DateDiff(“yyyy”,[BirthDate],[HireDate])
• DateAdd(Interval, Number, Date)

►
RetireDate: DateAdd(“yyyy”,25,[HireDate])
Customized Sorting
• Switch(expr1, value1, expr2, value2, etc.)

Switch([City]=“Seatle”, 1, [City]=“Redmond”, 2, etc.)
8
Access Queries: Dynamic Criteria

Parameterized Queries
►
Dynamic query based on varying criteria value
•
►
e.g. retrieve books written by a given author
Enter the parameter name in square brackets in criteria
•
•
Do not use existing field names
Can use expressions


e.g. Like "*" & [Last Name] & "*“
Query Criteria from Form Entries
►
Use a form to enter query parameter values
•
good for multiple parameter entries
1.
2.
3.
Create a parameter query
Create a form with unbound input control for each of query parameters
Add a command button that will run the parameter query
•
4.
Run Query Action of Miscellaneous Category
Reference the form controls that hold parameter values from the query
•
i.e. change the criteria to form controls
•
Parameter name = fully qualified name of form control
9
Access Queries: Joins

Inner Join
►
►

Left Outer join
►

Default join in Access (i.e. Natural Join)
Returns only the records where joined fields are equal in both tables
Returns all records from the left table
Right Outer join
►
Returns all records from the right table
10
Access Queries: Advanced Types

Action Queries
►
Append Query
•
►
Delete Query
•
►
Creates a new table from rows of other tables/queries
 will overwrite existing table of the same name
Crosstab Query
►

Modifies the values of particular fields for particular records
Make Table Query
•

Deletes table rows
Update Query
•
►
Appends table rows to an existing table
Performs mathematical operations on intersection of two fields
SQL-Specific Queries
►
Data-definition Query
•
►
Union Query
•
►
Defines/Changes the definition of a database object (e.g., create/modify a table)
Combines multiple SELECT queries
Pass-through Query
•
Send command directly to ODBC database server to run server-side SQL
11
Access Queries: Action Queries

Append Query  Appends table rows to an existing table
1.
2.
Create a select query.
Convert the select query to an Append query
•
3.
4.

Choose the destination fields for each column in the append query.
Run the query to append rows/records.
Delete Query  Deletes table rows
1.
2.
Create a select query.
Convert the select query to a Delete query.
•
3.

Delete Tool in Query Type group of Design tab
Run the query to delete rows/records.
Update Query  Modifies the values of particular fields for particular records
1.
2.
Create a select query.
Convert the select query to an Update query.
•
3.
4.

Append Tool in Query Type group of Design tab
Update Tool in Query Type group of Design tab
Set Update To: (and Criteria when appropriate) rows
Run the query to update fields/columns.
Make Table Query  Creates a new table from rows of other tables/queries
1.
2.
Create a select query.
Convert the select query to a Make Table query.
•
3.
Make Table Tool in Query Type group of Design tab
Run the query to update fields/columns.
12
Access Queries: Crosstab Query

Crosstab Query  Performs mathematical operations on intersection of two fields
►
Using the Crosstab Query Wizard
1.
2.
3.
4.
5.
6.
7.
►
Create a select query to join tables (if needed).
Click Query Wizard in the Other group of the Create tab.
Select Crosstab Query Wizard in the New Query dialog box & click OK.
Choose table/query with which to create a crosstab query & click Next.
Choose the field(s) whose values will be used as row headings & click Next.
Choose the field whose values will be used as column headings & click Next.
Choose a field and a function to use to calculate summary values.

The data type of the field that you select determines which functions are available.
Using the Crosstab Tool
1.
2.
Create a select query.
Convert the select query to a Crosstab query

3.
Set Row Headings

4.
Crosstab = Column Heading, Total = Group By
Set the calculation field and function

6.
Crosstab = Row Heading, Total = Group By, Sum, Avg, etc.
Set Column Headings

5.
Crosstab Tool in Query Type group of Design tab
Crosstab = Value, Total = Sum, Avg, etc.
Set Criteria to filter data (if needed).

Total = Where, Criteria = expression
13
Access Queries: SQL Queries

Data-definition Query  Defines/Changes the definition of a database object
►
Create a table
•
►
Modify a table
•

ALTER TABLE table_name
ADD/ALTER COLUMN field type(size)
DROP COLUMN field
Union Query  Combines multiple SELECT queries
►
Select queries must have the same fields (i.e., Union compatible)
•
1.
2.

CREATE TABLE table_name
( field1 type(size), field2 type(size), … , PRIMARY KEY (field))
SELECT field1, field2, …. FROM table1
UNION
SELECT fieldA, fieldB, …. FROM table2
Create the select queries in Design view
Copy & paste SQL statements into a union query
Pass-through Query  Send command directly to ODBC database server to run server-side SQL
1.
2.
Configure the server DBMS as an ODBC data source
Create a Pass-through query
14