Expression in forms
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From: Jamo on 7 May 2010 20:33 I am new to Access and I have a Table with a field called total.I have created a form to enter or modify data .I put an expression in the form in the Total field .The expression adds the results of several fields in the form and I want to add the total to the Table total field.The expression adds the field in the form but I can't get the field in the Table to update.I am not sure how do do this.not even sure what expression to write and where to put it .I gues what I am looking for is a clear step by step proceedure on how to do that. I realy need help
From: John W. Vinson on 7 May 2010 21:09 On Fri, 7 May 2010 17:33:01 -0700, Jamo <Jamo(a)discussions.microsoft.com> wrote: >I am new to Access and I have a Table with a field called total. Then you have an incorrectly structured table. The Total field should simply *not exist*. >I have >created a form to enter or modify data .I put an expression in the form in >the Total field .The expression adds the results of several fields in the >form and I want to add the total to the Table total field.The expression adds >the field in the form but I can't get the field in the Table to update.I am >not sure how do do this.not even sure what expression to write and where to >put it .I gues what I am looking for is a clear step by step proceedure on >how to do that. I realy need help Storing derived data such as this in your table accomplishes three things: it wastes disk space; it wastes time (almost any calculation will be MUCH faster than a disk fetch); and most importantly, it risks data corruption. If one of the underlying fields is subsequently edited, you will have data in your table WHICH IS WRONG, and no automatic way to detect that fact. Just redo the calculation whenever you need it, either as a calculated field in a Query or just as you're now doing it - in the control source of a Form or a Report textbox. -- John W. Vinson [MVP]
From: Jamo on 8 May 2010 09:06 -- Center for technica education "John W. Vinson" wrote: > On Fri, 7 May 2010 17:33:01 -0700, Jamo <Jamo(a)discussions.microsoft.com> > wrote: > > >I am new to Access and I have a Table with a field called total. > > Then you have an incorrectly structured table. The Total field should simply > *not exist*. > > >I have > >created a form to enter or modify data .I put an expression in the form in > >the Total field .The expression adds the results of several fields in the > >form and I want to add the total to the Table total field.The expression adds > >the field in the form but I can't get the field in the Table to update.I am > >not sure how do do this.not even sure what expression to write and where to > >put it .I gues what I am looking for is a clear step by step proceedure on > >how to do that. I realy need help > > Storing derived data such as this in your table accomplishes > three things: it wastes disk space; it wastes time (almost > any calculation will be MUCH faster than a disk fetch); and > most importantly, it risks data corruption. If one of the > underlying fields is subsequently edited, you will have data > in your table WHICH IS WRONG, and no automatic way to detect > that fact. > > Just redo the calculation whenever you need it, either as a > calculated field in a Query or just as you're now doing it - > in the control source of a Form or a Report textbox. > > -- > > John W. Vinson [MVP] > . > John: Thank you so much for the information. I will delete that field out of the table and create a report to do the total calculation, however for my own curosity can that be done what I was trying to do in a form? I will follow you advice and proceed from here
From: Linq Adams via AccessMonster.com on 8 May 2010 13:56 John's advice is spot on, of course, and should be followed in the vast majority of cases, including the scenario you have here. In the very few cases where storing a calculated value is necessary, you have to move the calculation to somewhere other than the Control Source for the textbox, so that the Control Source can be a field in the underlying table and theresults stored in that field. If, for instance, you were adding the values of two textboxes together, txtFieldA and txtFieldB, you'd do something like this, in the AfterUpdate event of each of them: Private Sub txtFieldA_AfterUpdate() Me.txtTotal = Nz(Me.txtFieldA, 0) + Nz(Me.txtFieldB, 0) End Sub Private Sub txtFieldB_AfterUpdate() Me.txtTotal = Nz(Me.txtFieldA, 0) + Nz(Me.txtFieldB, 0) End Sub -- There's ALWAYS more than one way to skin a cat! Answers/posts based on Access 2000/2003 Message posted via AccessMonster.com http://www.accessmonster.com/Uwe/Forums.aspx/access-forms/201005/1
From: John W. Vinson on 8 May 2010 19:51
On Sat, 8 May 2010 06:06:04 -0700, Jamo <Jamo(a)discussions.microsoft.com> wrote: > Thank you so much for the information. I will delete that field out of >the table and create a report to do the total calculation, however for my own >curosity can that be done what I was trying to do in a form? I will follow >you advice and proceed from here Well, you can't do calculations in tables - but you have at least three other choices! You can do a calculation in a Query by just typing the calculation expression in a vacant Field cell: Total: [FieldA] + [FieldB] Or you can display a calculation on a Form by putting an expression in the control source property of a form Textbox: = [FieldA] + [FieldB] The same technique works on a Report as well. If you want to sum the value of a field across multiple records, you can also do it three (or more) different ways: with a Totals Query; or in the Footer of a Form or Report: = Sum([FieldA]) So you're not losing much by being unable to do the calculation in a table. SideNote: Access 2010 has <sigh> calculated fields in tables. In reality they're a hidden query, and in fact this can be a useful technique, but you do need to understand the underlying logic. -- John W. Vinson [MVP] |