DB Implementation: MS Access Queries

MS Access Queries Database Queries What does it do? How does it work? Core DBA skill → A way of searching for & extracting data from tables table에서 data를 검색하거나 추출하는 방법 What does it do? Find target information → Retrieve, Filter, Sort, Aggregate/Summarize Manipulate data → Add, Change, Delete, Combine (& calculate) data in tables Assemble/Supply data → for Forms and Reports How does it work? Query object  SQL & a dynaset (“live” view of table) Data changes made in query is reflected in underlying tables Database Design

Access Queries: Views Datasheet view Design View For displaying the result of the query → Useful for reviewing/validating the query Design View For creating/modifying a query via drag & drop GUI Object Relationship Pane Add tables/queries Add fields to the Design Grid creation: CUSTOMER table multi-table query: PRODUCT+SUPPLIER qrySensless, qrySensible Design Grid Sort row → ascending/descending sort Show row → show/hide fields Criteria row → apply data filter Totals row → compute aggregate stats Database Design

Access Queries: Basic Types Simple Query Uses a single table/query To generate a subset (row/column) of a table Multi-table Query Joins multiple tables/queries Joining tables in Query Design does not permanently link tables Select Query Selects records that meet given criteria Criteria row ← Selection Criteria Parameter Query Prompts for query criteria values (parameters) to run a dynamic query Criteria row ← [Query Prompt] (or Search Form control name) update: publisher + publication set Available=No for publisher JimBob Publishing append crosstab how many works each producers produce in each category? Database Design

Access Queries: Sort & Filter Design View Sort using the Sort Row Sort priority is from left to right for multiple sort Filter using the Criteria Row AND query ← criteria in a single row OR query ← criteria in multiple rows Criteria in a single cell → AND/OR Query Criteria Determines which record to include “expressions” that consist of Constants (e.g., 2000, “Adams”) Operators (e.g., >, +, *, AND) Functions (e.g., DateDiff) Field references (e.g., [Lastname]) - Gcflearnfree.org - CUSTOMER wildcard: tblVoters Database Design

Access Queries: Query Criteria Date/Time fields Number fields Expression Returns Between #1/1/15# and #12/31/15# Dates from 1/1/2015 to 12/31/2015 > #1/1/15# After 1/1/2015 < Date() Before today DateDiff(“yyyy”,Date(),[Birthdate]) > 60 Over 60 years old DatePart(“m”, [Birthdate]) = 12 Born in December Expression Returns Between 10 and 20 Number from 10 to 20 >= 10 Greater than or equal to 10 10 Equal to 10 Not 10 Not equal to 10 Is Null No value is entered In (5,10,15) Number equal to 5, 10, or 15 Database Design

Access Queries: Query Criteria Text fields Expression Returns In (“John”, “Mary”, “Jane”) Equal to John, Mary, or Jane Like “J*” Starts with “j” Like “*s” Ends with “s” Like “*oh*” Contains “oh” Like “[A-C]??” Starts with A through C and has two more characters ???? Any 4 characters Len([LastName]) = Val(4) Any LastName of 4 characters Right([LastName],2) = “es” Any LastName ending in “es” (same as Like “*es”) Left([LastName],2)= “Ja” Any LastName starting with “Ja” (same as Like “Ja*”) Is Null No value is entered Is Not Null Value is not missing Not “James” Not equal to “James” Database Design

Access Queries: Expressions Using expressions to create a Calculated Field Enter expressions in blank column of query design view NAME: [Field1] operator [Field2] Examples Simple math DiscountPrice: [Discount] * [StandardPrice] String Concatenation Author: [FirstName] & “ ” & [Lastname] Date & Time math HireAge: DateDiff(“yyyy”,[BirthDate],[HireDate]) DateDiff(Interval, BeginDate, EndDate) RetireDate: DateAdd(“yyyy”,25,[HireDate]) DateAdd(Interval, Number, Date) Customized Sorting/Format Branch: Switch([City]=“Seattle”, 1, [City]=“Redmond”, 2, [City]=“New York”, 3) Switch(expr1, value1, expr2, value2, etc.) tbleCustomerDiscounts + tblPrices add Cname, discount, Stdprice Zoom Window (Shift+F2) Dolla Discount: [Discount]*[StandardPrice] Net Price: [Standardprice]-[dolla discount] new Q: add EMPLOYEE create name field Hireage: DateDiff(“yyyy”,[BirthDate],[HireDate]) Database Design

Access Queries: Sort & Filter Datasheet View Common Filters → Filter for specific values Click the icon on the right side of the field label Check the values for the filter OR Click the Range Filter (e.g. Date Filter) & specify the filter value Filter by Selection → Filter by selected value Select a specific value in the datasheet Right-click & select a filtering option CUSTOMER wildcard: tblVoters Database Design

Access Queries: Sort & Filter Datasheet View Filter by Form → Filter on several fields on a form Click Advanced in Sort & Filter group of Home tab Select Filter by Form Select multiple filter values as needed Advanced Filter → Define custom filters → Learn how to write query criteria Create a filter by Common Filter, Selection, or Form Select Advanced Filter/Sort CUSTOMER wildcard: tblVoters Database Design

Access Queries: Dynamic Criteria Parameter Queries Dynamic query based on varying criteria value Enter the parameter name in square brackets in criteria Do not use existing field names Can use expressions → e.g. Like "*" & [Last Name] & "*“ Database Design

Access Queries: Dynamic Criteria Query Criteria from Form Entries Use a form to enter query parameter values → good for multiple parameter entries Create a parameter query Create a search form with unbound input control for each of query parameters Add a command button that will run the parameter query Run Query Action of Miscellaneous Category Change the query criteria to search form control names Database Design

Access Queries: Joins Inner Join Outer join Default join in Access (i.e. Natural Join) Returns only the records where joined fields are equal in both tables Outer join Returns all records from one of the tables Theta Join: CHARTER & MODEL Database Design