Jan's Access Basics: Lookup Wizard

It is easy and usually painless to add or delete records from a table. But, changing the design of a table that already has records can be more of a problem. It depends on what kinds of changes you make. Let's look at some of the complications.

Changing Field Size

Example 1: Reduce field size safely-
In the Star Wars Collectibles table, the field size for the field Condition allows up to 50 characters. The values in this field come from a Lookup list: Mint, Excellent, Good, Fair, Poor. The longest value you can chose is the word "Excellent, which has 9 characters. You could safely change the length of the Condition field to 9. You would not lose any data. If you decided later to add other values to the list, you might need to increase the field's size.

Example 2: Reduce field size and lose data-
The field HowAcquired also allows up to 50 characters. The longest entry for this field that is actually used in the records is "Bought retail", which has 13 characters. (You must count spaces also.) If you reduce the field size to 9, some entries will lose those last 4 characters. That's a "whoops!" You really want to avoid throwing away your data!

Example 3: Available but not used-
You must look carefully at what the choices are, not just what you see in the records. For the field HowAcquired, one of the choices is "Bought at auction", which has 17 characters. No record is using this value yet. Looking at the records, you would not know that you need at least 17 characters. You cannot reduce the field size to the 13 needed for the existing data after all.

Example 4: Predicting the future
The field ItemName allows 50 characters but does not have a list to choose from. How many characters do you really need?? The longest entry now has 27 characters. But what about the future? You have to know how long future entries might be. You must be a prophet! Better to leave this kind of field with lots of space.

Changing a Field's Type

Sometimes changing a field's type is no problem. Sometimes it is disastrous. The data for that field may be cut short or even completely lost. Designing your tables right the first time works better!

Problem: Not allowed to change a field's type:
Cause: The field is part of a relationship with another table.
Solution: Delete the relationship first, make your changes, then recreate the relationship.

Lookup Wizard

It is always easier to pick from a list than to remember what the choices are! In the Table Design View, in the bottom section, each field has a Lookup tab. For some data types, like AutoNumber and Memo, the tab is blank because they cannot use a Lookup list.

When you create a Lookup list for a field, the list is available to you in a both the datasheet and form views.

Lookup Properties

The properties of the Lookup list are on the field's Lookup tab. You can set these properties yourself without going through the wizard, once you know what they are all about.

Table Design View: Lookup tab using list for row source

Display Control:
Text Box, List Box, or Combo Box
With a Combo Box control the table's designer can choose whether to allow new items or whether to require the user to choose only from the list. A Combo Box has more properties on the Lookup tab than a List Box.

The List Box will accept only items from the source. Automatically adding new items requires some programming.

Row Source = Value List:
The illustration shows that the Row Source for the field Condition is a simple list. You can edit the list here to add or remove any of the choices. Note the punctuation that is required!

Row Source = Table or Query:
The illustration shows that the Row Source for the field EpisodeID is a query that is saved as part of the definition of this table. The row source could have been another table or a query that is saved outside the table.

Bound Column: The data in the bound column of the row source is what is stored in this field in this table. Often you are storing the AutoNumber for a record in a different table.

Column Count: The number of columns from the row source to display in the drop list.

Column Heads: If it is not obvious what the values in the columns mean, you can show the field names as column heads.

Column Widths: You can set how much space to allow for each column in the drop list. You can save space in the list's display if you know what the widest item is.

List Rows: The number of rows from the row source to show at one time. A vertical scrollbar will appear if there are more items in the list.

Limit to List: For a combo box you can choose to allow entries that are not on the list. To automatically add such items to the list requires some programming code.

Step-by-Step: Lookup Wizard

What you will learn:

to change the data type for a field
to create a Lookup field with Lookup wizard
to view the Row Source query
to add data using a Lookup column

Start with: mytrips.mdb from previous lesson

Change Data Type

Why do you need to change a data type? To create a relationship between the tables Trips and Travel Agents, you need a shared field. Right now there is not one. By making a couple of changes you can make it possible to match fields from the two tables.

In the table Trips, you have a field called Travel Agent that is a memo field. You originally put agents' names, phone numbers, email addresses and other contact information in that field. That is the kind of information that is in the table Travel Agents. You are going to rename the field and change the field's type so that the tables can be related. All of the data in that field will be lost for all records! (In real life you would want to be sure you had a copy of all that was going to be lost!)

Open the table Trips in Design View.
Edit the name of the field to read AgentID to match the field in the Travel Agent table.
Change the data type for the Travel Agent field from memo to Number. The field size is set to Long Integer by default. That's what we want this time.
Edit the description to read AgentID from Travel Agents table.
Click on the Save button on the toolbar to save the changed table.

A message appears, warning you that data has been lost from fields in 8 records.

Which fields lose data? Unhappily, the message does not tell you from which field or if there are several that will lose data. In this exercise we touched just one field before saving. In real life you could easily make several changes to several fields, which would make this message very confusing.
Click on Yes to continue.
Click on the View button to switch to Datasheet View. The renamed field AgentID has no values any more.

Most of the trips did not use a travel agent and should remain blank. Three trips did have information about the travel agent. Those agents are listed in the Travel Agents table. You will need the AgentID for each of them. No one wants to try to remember such ID numbers! You will make changes to the field to allow you to pick from a list instead.

Table Datasheet View: AgentID field blank

Use the Lookup Wizard

In this section you will use the Travel Agents table as the source for the choices for a Lookup list. The Lookup Wizard makes it easy to create such a list.

Open the table Trips in Design View.
Click in the data type Number for the field AgentID. An arrow appears at the right of the cell.
Click the arrow to expand the list for data types.
Click on Lookup Wizard... at the bottom of the list.
The wizard opens.
In the first step, choose the first radio button, I want the lookup column to look up the values in a table or query.

If you had a short list that would not be needed for other tables, queries, forms, or reports, you could type in the list values instead.
Click on Next to advance to the next step.
Since there is only one other table in the database, it is already chosen for you. You are allowed to choose any table or query that is in the database, or a combination!
In the second step, Click on Next to advance to the next step.
In the third step, select AgentID and click the > button in the middle to move that field to the list of "Selected Fields" on the right.
Repeat to move LastName and then FirstName into the list on the right. (Yes, the order you do this is important!)
Click on Next to advance to the next step.
In the fourth step (which is not available in Access 2002), choose to sort first on LastName and then on FirstName, both in Ascending order.
This will sort the names in the usual alphabetical order.
Click on Next to advance to the next step.

Without the sorting, the names appear in the same order as they are in the Travel Agents table. It would have been nice if we had alphabetized before we entered the records. But then, if we added a new record later, the list would be no longer alphabetized anyway. Access 2003 added a nice feature when it added sorting in this wizard!
In the fifth step, leave the box checked for Hide key column.

This hides the AutoNumber field from the Travel Agents table. It's a boring number, but it is the value that is stored in the field you are creating, even though what you see is a name. A bit confusing but useful!

You can drag the columns wider or narrower in this window. We do not know how long the other agents' names are. You can leave the widths at the default size.
Click on Next to advance to the next step.
In step 6, type the label AgentID.
Click the Finish button.

Problem: AgentID already exists: An error message appears if you used the menu Insert | Lookup Wizard... , which tries to create a new field instead of modifying an existing field. Since there is already a field with this name, you would have to use a different name. You could then delete the previous field and rename the new one. You may have to close up the database before Access will let go of the deleted field's name and allow the name change. Annoying!
Click the Finish button again. A message appears. This is not an error. Part of the process of creating the Lookup list is to create a relationship between the table and the source you chose for the Lookup column.
Click on Yes.
The field AgentID looks the same. Where are the changes? On the Lookup tab!

View Row Source Query

The Lookup tab shows that the Lookup Wizard made a lot of choices for you.

The Row Source that the Lookup Wizard created is an SQL query, which will be saved in the Table Design itself. It will not show in the list of Queries in the Database Window.

Click on the Lookup tab and inspect the settings. The wizard did a lot of work for you!
Click in the Row Source. The 3 dots button appears at the right.
Click the dots button .
A Query Builder window opens, showing the Design View for this SQL statement.

This query selects the 3 fields to show in the Lookup list and sorts the list alphabetically.
Without the sorting, the agents would be listed in the order that they were entered into the database. The more items in the list, the more annoying this would be since they are not likely to be in alphabetical order!
From the menu select Query | Run .
The SQL statement is executed and you can see a datasheet of what it picks out for your new Lookup list.
Close the query window.

Use a Lookup List

Now you can use the Lookup list to pick the travel agents for the trips. Finally!

Switch to Datasheet View. Save the table again when you are prompted to do so.
Click in the AgentID field of record #2, the Alaska trip. An arrow appears at the right of the cell.
Click the arrow to open the list of choices. This is so cool!
While still in the AgentID field for the Alaska trip, click on the choice Martinez, Jorge.
The AgentID field now shows Martinez, which is the LastName value from the Travel Agents table. Showing just the LastName will be confusing if there are two agents with the same last name. A different query could solve this problem, but for now, we will accept what the wizard did.

Confusion: What you see is not quite what you get with Lookup fields.
- Lookup list shows several columns, but the datasheet can show only 1 column:
  The first column with a width greater than 0" will show in the datasheet. This is why the order was important when you selected the fields in the Lookup Wizard.
- What is displayed in a datasheet or form may not be what is actually stored in the table!
  The Bound column is column 1, AgentID. That is the value that is stored in the record. Since column 1 has a width of 0", the boring ID number is hidden from the list and display of the datasheet or form. The next column in the list shows instead, LastName.
  
  This can be confusing if you try to make some changes directly in the datasheet. Usually the table designer is showing you something that is more user-friendly than the usual ID number. If the field has a Lookup list, you really do need to use it and not type in values yourself.
To hide a column in a Lookup list: Set the column's width to 0". Check the Lookup tab for this field. This method is how the AgentID number was hidden in the Lookup list.
Avoid scrollbar in Lookup list: The List Width should be at least as wide as the total of the column widths. Otherwise you will see a horizontal scrollbar.
Similarly, select Martinez, Jorge as the travel agent for the Ireland trip.
Select Chavez, Hector as the travel agent for the Italy trip.
Close the Trips table.

Access Basics: Lookup Wizard

Changing Existing Fields