Functions & Concatenation
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FullName: [LNAME] & ", " & [FNAME] & " " & [MNAME]
MiddleInitial: Left([MNAME],1)
Image: "C:\Documents and Settings\mharris1\My Documents\AccessTraining\Photos\"
& [PAROLEE].[CDCNUM] & ".jpg"
AGE: DateDiff("yyyy",[DOB],Date())IIf(Format([DOB],"mmdd")>Format(Date(),"mmdd"),1,0)Weekday:
Weekday([LASTCHANGEDATE])
WeekdayName: WeekdayName(Weekday([LASTCHANGEDATE]))
Month: Month([LASTCHANGEDATE])
MonthName: MonthName(Month([LASTCHANGEDATE]))
Year: Year([LASTCHANGEDATE])
Better Policing with Microsoft Office
Mark Stallo & Chris Bruce
Expressions, Functions, and Calculations
As we learned when we were setting table validation rules back at the beginning of this chapter, expressions are
combinations of field values, operators, and functions that produce a result. Functions are pre-programmed
commands that return a value based on a calculation or other operation.
Expressions and functions greatly enhance your ability to manipulate data. We are going to look at a wide
variety in this section.
»Step 1: Create a new query (Create | Other |Query Design). Add the “Incidents” table and
close the “Show Table” box.
Expressions, functions, and calculations are typed in the “Field” row of the design grid, as an alternative to
double-clicking on a field and adding it. The simplest expressions do nothing more than re-name an existing
field. For instance, the field named “DateOfReport,” while descriptive, is fairly clunky. The readers of our
reports may want something simpler.
»Step 2: In the blank “Field” row of the first column, type: Date: DateOfReport (Figure A-89).
If you switch to Datasheet View, you will see that the column that normally would have a “DateOfReport”
heading now simply reads “Date.”
Figure A-89: this simple expression simply renames the “DateOfReport” field
All expressions are preceded with the name of the resulting field and a colon. We will see more examples.
More advanced expressions concatenate or combine multiple fields.
»Step 3: In the blank “Field” row of the second column, type: Address: [StNo] & " " & [Street1]
(Figure A-90). Make sure you put a space in between those quotation marks.
This expression sticks the address number and street name in a single field called “Address,” with a space
between them. The brackets indicate field names—if you don’t type them, Access will insert them itself. The
ampersands (&) are operators that tell Access to concatenate: take the “StNo” field and a space (in quotes) and
the “Street1” field.
Figure A-90: concatenation expression design and result
Now it’s time for some functions, which manipulate existing data in new ways. There are numerous functions
available in Access; many are listed in Table A-8. Some of the most valuable extract parts of dates.
»Step 4: In successive blank “Field” rows, enter the following functions:
Year: Year([DateOfReport])
Month: Format([DateOfReport],"mmm")
Year-Month: Format([DateOfReport],"yyyy-mm")
Figure A-91: three functions that re-arrange or extract parts of the date…
Figure A-92: …and the results
The YEAR and FORMAT functions illustrate function syntax. Functions are always followed immediately by
a set of parentheses. Inside the parentheses is the name of the field that the function applies to. If there are
any arguments required for the function, these follow the field name after a comma. Some functions, like
YEAR, have no arguments—just the field name that contains the date from which the year is to be extracted.
Others, like FORMAT, have one argument—the nature of the format. Some functions have multiple
arguments (see Table A-8).
A small number of functions, like NOW (calculates the current date and time) and DATE (calculates the
current date) have nothing inside the parentheses—you just open and close them: DATE(). The parentheses
are still necessary to tell Access that you’re using a function instead of, for instance, a field name called
“Date.”
We will do more with date functions during the next lesson on cross-tabulation. For now, we’ll move on to
another function and calculation.
»Step 5: Close this query. Save it if you want to refer back to it later.
»Step 6: Select your “Larceny Arrests at the Metropolis Mall” query and open it in Design View.
We already used filtering and aggregation to determine the most likely towns of residence for our mall
thieves. Now let’s take a look at their ages. There is no “Age” field, but we can calculate the individual’s age,
at the date of offense, based on his or her date of birth.
»Step 7: Select the “Town” field by clicking on the thin gray selector bar above it. Hit the DELETE
key to remove it from the query.
»Step 8: In the nearest blank column to the right, type the following in the “Field” row:
Age: INT(([DateOfReport]-[DOB])/365.25)
(Look at the expression carefully to make sure you see the difference between parentheses and brackets.
Parentheses follow functions and enclose their arguments; brackets surround field names.)
This expression is two calculations within a function. Let’s break it down.
[DateOfReport]-[DOB] subtracts the person’s date of birth from the date of the report. This provides the
person’s age in days.
([DateOfReport]-[DOB])/365.25 takes this age in days and divides it by 365.25 to give us the age in years
(the .25 accounts for leap years). The parentheses are necessary to tell Access to perform the subtraction first;
otherwise, by normal order of operations, it would perform the division first.
We could go with this calculation alone, but the result would be a ridiculously precise age, down to the
nanosecond (e.g., 32.78493910). The INT function strips away the decimals and gives us a straight integer.
(We wouldn’t want to use a ROUND function, because someone who is 36.99999 is still considered 36 until
he reaches his 37th birthday.) So we enclose the entire calculation within the opened-and-closed parentheses
of the INT function to achieve our result.
»Step 9: Switch to Datasheet view and see the result. Re-arrange the order of the columns so that the
age comes first, and sort ascending
by this column.
Figure A-93: the “Age” calculation within our design grid, and the result
Table A-8: Common Functions in Microsoft Access
For the purposes of these examples, assume that we have a table containing an incident number, a date, a time, a crime,
a street number (“STNO”) and a street. Assume that the current date is 05/29/2009. The records that we’ll use for most
of the examples looks like this:
INUM
I0902150
I0907151
DATE
02/15/2009
06/24/2009
Function
DATE
Use/Parameters
DATEVALUE
DAY
FORMAT
Returns the current date
Forces access to
recognize a field or
expression as a date.
Use this when you want
to build another query
that does calculations or
performs functions on
the date field.
Returns the numeric day
from a date field
Re-formats the a
date/time (or part of it)
to whatever you desire.
Requires a parameter
(after the comma) that
specifies what you want
TIME
19:24
09:30
CRIME
ROBBERY
BURGLARY
STNO
120
500
Examples…
DATE()
…Returns
05/29/2009
DATEVALUE(“01/01/2009”)
01/01/2009
DAY([Date])
15
24
FORMAT([Date],"mmm")
Feb
Jun
FORMAT([Date],"mmmm")
FORMAT([Date],"ddd")
FORMAT([Date],"dddd")
FORMAT([Date],"yyyy")
February
June
Sun
Wed
Sunday
Wednesday
2009
2009
STREET
Ash St
Main St
Function
Use/Parameters
Examples…
FORMAT([Date],"yyyymmdd")
FORMAT([Date],"ddmmmyy")
HOUR
IIF
INT
LCASE
LEFT
LEN
MID
Extracts the hour of day
from the time.
Allows you to create a
series of values based
on criteria in your fields
Chops off decimal
places from a number
Converts a text field to
lower case
Takes the specified left
number of characters
from a field
Shows you the number
of characters in a text
field
Returns the specified
number of characters
from a specified point
in a text string.
HOUR([Time])
IIF([Time]>=#07:00:00# and
[Time]<#19:00:00#,"Day","Night”)
Night
Day
INT(23.693940)
23
LCASE([Crime])
robbery
burglary
LEFT([CRIME],3)
ROB
BUR
LEN([Street])
6
7
MID([Crime],2,4)
OBBE
URGL
h
in
24
30
2
6
MID([Street],3,2)
MINUTE
MONTH
NOW
RIGHT
ROUND
TRIM
UCASE
Extracts the minute
from the time
Returns the numeric
month from a date field
Returns the current date
and time. Useful for
calculations. When used
in calculations,
calculates by day.
Takes the specified left
number of characters
from a field
Rounds a field or
calculation to a specified
number of digits.
Removes spaces from
the beginning and end
of a text string. Useful
for cleaning addresses
for geocoding.
Turns lower case into
upper case text
…Returns
20090215
20090624
15FEB09
24JUN09
19
9
MINUTE([Time])
MONTH([Date])
NOW()
05/29/2009
18:39
NOW()-[Date]
103.78
-25.22
RIGHT([Crime],3)
ERY
ARY
ROUND(NOW()-[Date],0)
104
-25
ROUND(NOW()-[Date],1)
103.8
-25.2
TRIM(" 150 Main St
150 Main St
UCASE([Street])
")
ASH ST
MAIN ST
Function
WEEKDAY
Use/Parameters
Gives the numeric
weekday based on a
parameter. For
1=Sunday, the
parameter is 1. For
1=Monday, the
parameter is 2.
Examples…
…Returns
WEEKDAY([Date],1)
1
4
WEEKDAY([Date],2)
YEAR
Returns the year from a
date field
YEAR([Date])
7
3
2009
2009
Access has never documented its functions very well, but Access 2007 has better documentation than
previous versions. One way to determine the uses and syntax of a function is to use Access’s otherwise fairly
useless Expression Builder. Right-click on an empty Field row in a query, choose “Build,” double-click on
“Functions” and then “Built-In Functions.” On the right-hand side, select a function you’re curious about
and click the “Help” button. A small browser window will open with information about that function.
Figure A-94: using the Expression Builder to learn more about functions
You can use functions and expressions in reports as well, by creating a text box and entering the expression
where you would normally enter the field name. The one difference in syntax is that instead of beginning the
expression with the name of the resulting field and a colon, you begin with an equals sign (=).
Figure A-95: using an expression in a report