Query Criteria Combo Box

2020. 1. 23. 20:53카테고리 없음

Query Criteria Combo Box

Give the combo box a unique name. By unique, I mean a name that isn’t the same as any other c0ntrol in the database. In the criteria for the query that populates your report, enter the expression Forms!form name!combo box name. The keyword Forms tells Access “Look on form name and fetch the value named combo box name. Mar 12, 2012  On this form you will need to place three objects, A combobox control that will be used to select the query criteria, and two command buttons, one to accept the selection, and one to cancel the form. Your completed form will probably look something.

This is such a frequent request that literally hundreds of pages can be found describing one technique or another to achieve the desired result. I particularly like one example from Microsoft, which is by far the most convoluted solution I have ever seen, although it is remarkably generic as well. At the time of writing, a user comment on the page expresses the general feeling: “why does such a simple thing require 50 lines of code?”The vital question that is often overlooked, or asked only in passing is: “why do you need this option, and how do you intend to use it?” Depending on the answer, the solution can be surprisingly simple.The aim of the article is to show not one but several solutions to the request itself, and to concentrate equally on the way the “all” option is used.A very simple demo file is included, but the article is hopefully understandable without downloading it. Note: The database in in Access 2000 format, but was created in Access 2007.

Create An Interactive Access Form To Filter A Query

After opening the database in an earlier version, if the demo doesn't work, please remove any missing reference: from Visual Basic Editor, choose (Tools References) and uncheck any libraries marked as missing. Then find and check both libraries named “Microsoft DAO?? Object Library” and “Microsoft ActiveX Data Objects?? Library”; use the highest version if you find several versions.Look! The option is already there!A combo box can take all the values from the list, but it can also be left blank. The control will have the default value Null, and the combo will display nothing.

A user can be instructed to delete the entry as well, provided this value — Null — is handled in a meaningful way by the application.The main objection to this idea is that the combo box should display something at all times, to keep the user informed. I don't agree with this, and rather like empty controls when I have no particular need for them, but that's not the point. If the combo box displays its bound column, say a country code or the name of a category, there is an easy solution. The format “@;;(all)” will display “(all)” instead of nothing when the control's value is Null.The same works for text boxes, incidentally, with the quite useful version “@;;Blue(last name — required)”. If the bound column is a number, the formatting string would be “0;;;0” to display zero when the field is blank. When the value is used, Nz can convert Null to zero.If the bound column isn't displayed this trick doesn't work, because the formatting is ignored.

One could use conditional formatting to change the background colour, but that doesn't replace an explicit message in the control.In any case, Null is a valid value unless it's prohibited by a validation rule or automatically changed through a Visual Basic event handler, typically `after update´.Using Null to mean “all”When controls on a form are used as criteria in a query, Null values usually break the mechansim. This is the reason for the vast majority or requests to add “all” as an option. The query looks perhaps like this. SELECT ProductID, ProductNAme, CategoryIDFROM ProductsWHERE CategoryID=Forms!frmFilter s!cboCateg oryAND.In the query design grid, this becomesField: CategoryID ProductName Table: Products Products Show: x x Criteria: Forms!frmFilters!CategoryID Like Nz(Forms!frmFilters!txtName,'.' )Select allI added a second column for a similar criteria using Like. It is believed that “like '.'

” returns all records, and the requested “all” option is often used to write an asterisk. In fact, this criteria returns only non Null values, which might be irrelevant when filtering on required fields, but is wrong as a generic solution.Anyway, it is difficult to modify the criteria to allow records matching a specific criteria from a control or all records when the control is Null. Many apparently good solutions will totally mess up the query grid when the query is next opened.

How To Create Search Form Using Combo Box

The demo file contains one query that looks perfectly reasonable in SQL view, but gets totally mangled by the query design grid. There is a good reason for that, and it must be accepted as an intrinsic limitation of the entire “criteria grid” concept.To maintain compatibility with the query design grid, the trick is to switch the criteria and the field, like this:Field: Forms!frmFilters!CategoryID Forms!frmFilters!txtName Table: Show: Criteria: Is Null Or CategoryID Is Null Or ProductNameSelect all Note: add other columns without a criteria to display these fields, if needed.This syntax really returns all records when a control is Null, even when a field is itself Null, and doesn't mess up the query grid. This trick is not nearly as useful for queries written and maintained completely in SQL view, naturally.Once you know how to create a criteria where Null means “all”, you might no longer need the additional row in your combo boxes.

Simply add this message: “A blank filter means that you do not want to filter on this field; use Del to delete the value from a combo box.”But I still want an “all” option!Perhaps also “none”, “all active products”, “VIP only”, etc. It does make sense to offer in the same combo box individual choices as well as some predefined global filters.Static Value ListsThis is the simple case.

If the row source is static, you simply add the options in the list, and you are done. You will need to handle the additional cases, but it's no longer a combo box problem.From Visual Basic, you also have the AddItem method, which you can use to add options dynamically, at any position in the list.Using SQLThis is the most frequent answer, found as solution in numerous questions here on EE as well. To implement this solution, the query needs to be updated in SQL view. For many Access users, this is the first time they have to do so, but it isn't as hard as it might look.If the query showing the list of categories looks like this. SELECT CategoryID, CategoryNameFROM CategoriesUNIONSELECT Null, '(all categories)'FROM CategoriesORDER BY CategoryIDThe first lines are left as they are.

The UNION operator introduces a new query (there can be several, each preceded by UNION) which needs to have the same number of columns, but not column names (they are ignored). Ideally, the data type should match, or the entire column will be treated as text.

Access

This isn't a problem with combo boxes, because all columns will be treated as text anyway, but it might alter the sorting of the records.The second FROM clause is not really used. It is a dummy because neither expression in the SELECT clause uses any field from the table. Any table will do, but the FROM clause is required.

Only one record is created here, as if the query had the DISTINCT option. This is a side effect of the UNION operator, which makes the entire query DISTINCT (meaning “distinct values”).To remove this side effect (not here, it's quite useful in our case) the operator UNION ALL can be used instead.The last line is the original ORDER BY clause, which will still work because the name of the columns are determined by the first query. Note that the “(all categories)” row will be sorted first because Jet always sorts Nulls first. Null also doesn't alter the data type: it is compatible with all types.Generating a Value ListSome people are more familiar with Visual Basic than with SQL. In order to gain full control over the row source, it is possible to replace the Table/Query row source with an equivalent Value List. The examples below are executed while the form is loading, and replace the query of a combo by an equivalent value list.' Uses a reference to “Microsoft DAO??

Object Library” Private Sub FormLoad Dim strList As String strList = ';(all categories);' With cboCategory With CurrentDb.OpenRecordset(.RowSource) Do Until.EOF strList = strList &!CategoryID & ';' &!CategoryName & ';'.MoveNext Loop End With.RowSourceType = 'Value List'.RowSource = strList End With End SubSelect all ' Uses a reference to “Microsoft ActiveX Data Objects?? Library” Private Sub FormLoad With New ADODB.Recordset.Open cboCategory.RowSource, CurrentProject.Connection, adOpenStatic cboCategory.RowSourceType = 'Value List' cboCategory.RowSource = ';(all categories);' &.GetString(ColumnDelimeter:=';', RowDelimeter:=';') End With End SubSelect allThere are many variations to these examples. Depending on the data, it might be necessary to quote text columns: “'red';'green';'blue'” instead of “red;green;blue”; Null values might require special treatment; certain fields should probably be formatted explicitly; etc.

If you need help implementing this code, it is best to ask a new question with a reference to this article (and not in the comments section below, thank you!)In any case, if the list displayed in the combo does not change during the life of the form, creating a static value list offers the most control and is quite often the most efficient also (in terms of speed and resources). The advantage over an entirely static list is that the row source is examined once, so that any changes in the base table(s) is visible the next time the form is opened, without any recoding.List-fill User Defined FunctionThe page mentioned in the introduction does just that. There are simpler variants, and versions managing more than one list at a time; they are also the most versatile for example when dealing with external data sources or stored procedures, but I don't have anything more to say about them in this article.Why doesn't the “all” option stick?Although the option has now been added, and is selectable in the combo box, it doesn't “stick”. The value is simply cleared, and no message remains. (You can observe this in the demo database, if you wish.)In the examples above, I have always associated Null or a zero-length string (ZLS) to “all”.

Due to the mechanics of a combo box, this value can never be selected or rather appear to be selected in the drop-down section. In other words, it works (Null is selected), but the visual feedback is not what it should be. The reason is that, in order for a row to be visibly selected, it needs to have a bound column matching the current value.In practice, it is perfectly logical to have an option in a combo box to clear it. If the fingers are on the keyboard, the Del key is used, if the hand is over the mouse, “all” (or “none”) can be selected with the same result.If “all” — or rather a message like “(all categories)” — should always be visible, this requires a few additional steps.

Access for Office 365 Access 2019 Access 2016 Access 2013 Access 2010 Access 2007When entering data on forms in Access desktop databases, it can be quicker and easier to select a value from a list than to remember a value to type. A list of choices also helps ensure that the value entered in a field is appropriate. A list control can connect to existing data, or it can display fixed values that you enter when you create the control. Read on to learn about the list controls available for Access forms, and how to create and customize them. What do you want to do?Learn about the types of list box controlsAccess provides two list controls for forms — the list box and the combo box.List box The list box control displays a list of values or choices. The list box contains rows of data, and is usually sized so that several rows are visible at all times.

The rows can have one or more columns, which can appear with or without headings. If the list has more rows than can be displayed in the control, Access displays a scroll bar in the control. The user is limited to the choices given in the list box; it is not possible to type a value into a list box.Combo box The combo box control provides a more compact way to present a list of choices; the list is hidden until you click the drop-down arrow. A combo box also gives you the ability to enter a value that is not in the list.

In this way, the combo box control combines the features of a text box and a list box.1. Click the arrow to display the drop-down list.2.

Click an option in the drop-down list.List boxes and combo boxes can be bound or unbound controls. These controls can look up values in a fixed list that you type yourself, or they can look up values in a table or query.

To create a bound list box or combo box that looks up values in a table or query, make sure the form is based on a record source that includes a foreign key field or Lookup field. This makes it possible to create the relationships that are needed to link the data in the list box or combo box to the data on the form.Create a list box or a combo box by using a wizard.Right-click the form in the Navigation Pane, and then click Design View.

Note: This procedure assumes that the form is bound to a table or query. Some of the steps will not apply if the form is unbound. To determine if the form is bound to a table or query, press F4 to display the property sheet. Tip: To change a combo box to a list box (or vice versa), right-click the control, click Change To on the shortcut menu, and then click the control type you want.Create a list box or a combo box without using a wizardWhen you create a list box or combo box without using a wizard, you set many of the properties of the control yourself. Note: In a combo box, the first visible column is displayed in the text box portion of the combo box when the list isn't displayed.

For example, the SupplierName column in the previous example would be displayed because the SupplierID column is hidden. If the SupplierID column was not hidden, it would be displayed instead of the SupplierName column.Add column headings to a combo box on a form.In the Column Heads property box, click Yes to display column headings. Headings in combo boxes appear only when the list is open.If the combo box or list box is based on a record source, Access uses the field names from the record source as the column headings.

Query Criteria Combo Box