Warning: strtotime() [function.strtotime]: It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/New_York' for 'EST/-5.0/no DST' instead in /home/frodr/public_html/msofficetuneup.com/wp-includes/functions.php on line 35
Warning: date() [function.date]: It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/New_York' for 'EST/-5.0/no DST' instead in /home/frodr/public_html/msofficetuneup.com/wp-includes/functions.php on line 107
Warning: date() [function.date]: It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/New_York' for 'EST/-5.0/no DST' instead in /home/frodr/public_html/msofficetuneup.com/wp-includes/functions.php on line 109
Warning: date() [function.date]: It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/New_York' for 'EST/-5.0/no DST' instead in /home/frodr/public_html/msofficetuneup.com/wp-includes/functions.php on line 111
Warning: date() [function.date]: It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/New_York' for 'EST/-5.0/no DST' instead in /home/frodr/public_html/msofficetuneup.com/wp-includes/functions.php on line 112
Mar
Warning: strtotime() [function.strtotime]: It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/New_York' for 'EST/-5.0/no DST' instead in /home/frodr/public_html/msofficetuneup.com/wp-includes/functions.php on line 35
Warning: date() [function.date]: It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/New_York' for 'EST/-5.0/no DST' instead in /home/frodr/public_html/msofficetuneup.com/wp-includes/functions.php on line 107
Warning: date() [function.date]: It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/New_York' for 'EST/-5.0/no DST' instead in /home/frodr/public_html/msofficetuneup.com/wp-includes/functions.php on line 109
Warning: date() [function.date]: It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/New_York' for 'EST/-5.0/no DST' instead in /home/frodr/public_html/msofficetuneup.com/wp-includes/functions.php on line 111
Warning: date() [function.date]: It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/New_York' for 'EST/-5.0/no DST' instead in /home/frodr/public_html/msofficetuneup.com/wp-includes/functions.php on line 112
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Access makes it remarkably easy to join two tables. The first step’s adding both tables to your query, using the Show Table dialog box. If you’re creating a new query in Design view, then the Show Table dialog appears right away. If you’re working with a query you’ve already created, then make sure you’re in Design view, right-click the window, and then choose Show Table.
If you’ve already defined a relationship between the two tables (using the relationships window, as described in Section 5.2), then Access uses that relationship to automatically create a query join. You’ll see a line on the diagram that connects the appropriate fields, as shown in Figure 6-14.
Figure 6-14. Access automatically joins the CustomerID field in the Orders table to the ID field in the Customers table, based on the relationship that’s defined in the database.
If you haven’t already defined a relationship between the two related tables, then you probably should, before you create your query (see Chapter 5 for full instructions). But if for some cryptic reason you’ve decided not to create the relationship (perhaps the database design was set in stone by another, less savvy Access designer), then you can manually define the join in the query window. To do so, just drag the linked field in one table to the matching field in the other table. You can also remove a join by right-clicking the line between the tables, and then choosing Delete.
Note: If you add two unrelated tables, then Access tries to help you out by guessing a relationship. If it spots a field with the same data type and the same name in both tables, then it adds a join on this field. This action often isn’t what you wantfor example, many tables share a common ID field. Also, if you’re following the database design rules from Section 2.5, then your linked fields have slightly different names in each table, like ID and CustomerID. If you run into a problem where Access assumes a relationship that doesn’t exist, then just remove it before adding the join you really want.
| UP TO SPEED Relationships vs. Joins |
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It’s important to understand the differences between a relationship and a query join.
If you have a relationship in place, then Access assumes you’ll want to use a join to link those tables together in a query, which only makes sense. |
Once you have your two tables in the query design window and you’ve defined the join, then you’re ready to choose the fields you want. You can pick fields from both tables. You can also add filter conditions and supply a sort order, as you would with any other query. Figure 6-15 shows an example of a query that uses a join, and Figure 6-16 shows that same query in action.
Note: When you have two linked tables, it’s easy to forget what you’re showing. If you join the Orders and Customers tables, and then select fields from each, then what do you you end up with: a list of classes or a list of instructors? Easy, you get a list of orders, complete with customer information. Queries with linked tables always act on the child table and bring in additional information from the parent.
Figure 6-15. This query shows information from the Orders and Customers tables. It doesn’t matter whether the first field’s from the Orders or Customers tableeither way, you’re creating a list of orders with added customer information. Notice how the Table box (under the Field box) shows which table each field comes from.
Figure 6-16. You can easily see at a glance who ordered what. The ID column’s the order ID (although you could display the IDs from both the Customers and Orders tables).
Note: When you perform a join, you see repeated information. If you join the Customers and Orders tables, you see the first and last name of a shopaholic customer appear next to several orders. However, this doesn’t violate the database rule against duplicate data. Even though the customer details appear in more than one place in the query results, they’re stored only once in the Customers table.
Remember, when you link a parent and child table with a join query, you’re really performing a query that gets all the records from the child table, and then adds extra information from the parent table. For example, you can use a join query to get a list of orders (from the child table) and supplement each record with information about the customer that made the order. No matter how you create the join, you won’t ever get a list of customers with order information tacked onthat wouldn’t make sense, because every customer can make multiple orders.
Joins are one of the most useful features in any query writer’s toolkit. They let you display one table that has all the information you need.
Warning: When using more than one table, there’s always a risk that two tables have a field with the same name. This possibility isn’t a problem if you don’t plan to show these fields in your query, but it can cause confusion if you do.
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