sometimes you may decide that you want
to add or modify fields in your tables
access makes it easy to do this although
there are some important things that
you'll need to consider there are three
different rules that you can apply to
control the type of data that the fields
can accept and these are data types
character limits and validation rules
to get started make sure that you have a
table open I'm using the customers table
we're going to scroll all the way to the
right until you see a blank field that
says click to add and when you click on
it you'll see a list of all of the data
types that you can choose from text is
the default option and this is the type
that you'll use for regular text such as
a person's name or address you'll also
use it for numbers that aren't used in
calculations like a phone number or zip
code for any numbers that you might want
to do calculations with you'll need to
choose number for example we would use
this for the quantities of an item that
we're sold if you're dealing with money
then you'll choose currency and if you
choose date and time then when you're
editing that field you'll see a calendar
icon which you can click to select a
date but in this case I just want a
simple yes or no answer so I'll choose
this one and this adds a checkbox for
each record then you can type in the
name of your field I'm going to name it
add to mailing list
then I'll resize this field
now we can just check each customer who
wants to be on our mailing list and you
can also click and drag the name to move
the field wherever you like if you
decide that you need a different data
type for a field then you can just
select it and then go to the fields tab
and click the data type drop-down arrow
I'm going to change this to text so I
can add additional information in this
field some of our customers want to
receive our weekly newsletter but others
just want to hear about our special
events now you should be very careful
about changing the data type because it
is possible to lose some of your data if
you change it to the wrong type in some
fields you may want to narrow down the
data even further by adding a character
limit and you can only do this with text
fields for example we want all of the
states to be formatted the same way so
we're only using the two-letter state
abbreviations if some of the records say
in C and others say North Carolina then
access won't know to group them together
which means our sorts filters and
queries may not work right in the fields
tab find the field size box the default
field size is 255 characters but I'm
going to change it to 2
and you may get a warning message here
so if you're sure you want to change the
field size click yes in this case
setting a character limit isn't quite
good enough because somebody could still
type a two letter code that's not a real
state for example in X to prevent that
we need to be a lot more specific about
what types of input this field will
accept and we'll do that by adding a
validation rule in the fields tab go to
the validation command on the far right
and select field validation rule
here I'm going to type each state
abbreviation in quotation marks and I'm
separating each one with the word or and
this may take a while so this expression
is just looking for exact matches but if
you want you can create validation rules
using the same syntax as that we talked
about in the query lessons for example
you could use the like syntax to set a
validation rule that only allows text
that ends with cake or if you're using
numerical values you could use greater
than to make sure that none of our
quantities are negative when you're done
click OK
whenever you create a validation rule
it's important to create a validation
message and this option is also under
the validation command this message will
pop up whenever somebody tries to type
in something that doesn't follow the
validation rule the message should
briefly describe the rule so that the
user can then make the necessary
Corrections in this case I'll just
mention that it needs to be a two letter
abbreviation
now you won't need to add a character
limit or validation rule to all of your
fields but you can add one or both of
them whenever you want to control the
types of information that your field
will accept like what you just saw radix
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