day 17: access chapter 2-3 rahul kavi [email protected] [email protected] october 17,...
TRANSCRIPT
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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
