DAY 17: ACCESS CHAPTER 2-3 RAHUL KAVI October 17,

LAST CLASS Relationship Types –Many-to-one –One-to-one –Many-to-many Calculated Fields Relationship Manager 2

TODAY’S CLASS Queries Calculated Fields in Queries Basic Queries Multi-table queries 3

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

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) 5

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 6

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) 7

FUNCTIONS Like Excel, Access has many functions for performing calculations –PMT –IIF –DateDiff 8

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) 9

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 10

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 11 yyyyYear qQuarter mMonth yDay of year dDay wWeekday wwWeek hHour nMinute sSecond

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 12

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 13

GROUP BY Group By groups the data before the aggregation functions are applied This allows you to find summary statistics for each group 14

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 15

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 16

NEXT CLASS Expression Builder Forms –Create, modify –Sorting –Form Sections –Control Types Reports –Create, modify –Sorting –Report sections –Control Types 17