DAY 17:ACCESS CHAPTER 2-3

RAHUL KAVIRahul.Kavi@mail.wvu.eduOctober 17, 2013

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LAST CLASS

• Relationship Types– Many-to-one– One-to-one– Many-to-many

• Calculated Fields• Relationship Manager

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TODAY’S CLASS

• Queries• Calculated Fields in Queries• Basic Queries• Multi-table queries

QUERIES

• A Query is a question one asks about the data stored in a database

• Access responds by displaying specific records that answer the question

• In creating a query, we tell access which fields are needed(in one or more tables) and what criteria needs to be met

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CALCULATED FIELDS IN QUERIES

• New fields can be calculated from existing fields using an expression

• Expressions can include the following:– Identifiers (names of fields)– Arithmetic operators (*, +, etc.)– Functions (Date(), IIf())– Constants (numbers such as 12 or 0.35)

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EXPRESSION SYNTAX

• You should give calculated fields a name by prefixing the expression with the name followed by a colon

• Example:– NewBalance: [Balance] + [MonthlyInterest]

• After the colon, you can use any functions or mathematical operators to calculate the value based on existing fields and/or constants

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EXPRESSION BUILDER

• Right click the field->Builder• Select the field, then

– Query Tools->Design->Query Setup->Builder• Expression builder provides graphical

tools for looking up operators (functions and arithmetic operators) and operands (existing fields, constants)

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FUNCTIONS

• Like Excel, Access has many functions for performing calculations– PMT– IIF– DateDiff

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PMT

• Identical to PMT in Excel– Pmt(rate, num_periods, present_value)

• Rate is the interest rate per payment period• Num_periods is the number of payment periods• Present_value is the present value of the loan

(which should be negative for most situations)

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IIF

• IIF is the Access equivalent of IF in Excel• Iif(expression, truepart, falsepart)

– Expression is a comparison that is evaluated– If expression is true, Iif returns the value of

truepart– If expression is false, Iif returns the value of

falsepart

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DATE ARITHMETIC• Date()- returns the current date• Now()- returns the current date

and time• DateDiff(format, date1, date2)

– Format: Result in years, seconds, quarters, etc

– Date1 and Date2 specifies the date for which the difference has to be calculated

yyyy Yearq Quarterm Monthy Day of

yeard Dayw Weekdayww Weekh Hourn Minutes Second

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AGGREGATION (SUMMARY QUERIES)

• Summary queries allow you to calculate summary statistics from your data– Avg, Count, Max, Min, StDev, Var, Sum

• These functions can be used as calculated fields

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TOTALS QUERIES

• Aggregation can also be done as a totals query

• Query Tools->Design->Show/Hide->Totals• Select how you would like to aggregate

each field

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GROUP BY

• Group By groups the data before the aggregation functions are applied

• This allows you to find summary statistics for each group

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LOOKUP FIELDS• Lookup fields are a nice way of hiding the

foreign keys• Instead of displaying the foreign key, the lookup

field looks up the record for that key and displays whatever fields you set up

• Lookup fields also provide a dropdown to select the record you want to establish the relationship with

• Internally, it is still just stored as the foreign key

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CALCULATED FIELDS

• Calculated fields can also be added to table definitions for commonly used calculations

• Simply select Calculated as the field type and input your expression into expression builder

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NEXT CLASS• Expression Builder• Forms

– Create, modify– Sorting– Form Sections– Control Types

• Reports– Create, modify– Sorting– Report sections– Control Types