How to Create a Relationship in Access | tankekraft.info
Click Create. Access draws a relationship line between the two tables. If you selected the Enforce Referential Integrity check box, the line appears thicker at each. If you do not find a relationship between the two tables, create one by dragging a field from one of the tables to a field on the other table. The fields on which you. This article describes how to define relationships in a Microsoft Access database. The article includes the following topics: What are table.
The Field List pane shows fields available in related tables and also fields available in other tables in the database.
When you drag a field from an "other" unrelated table and then complete the Lookup Wizard, a new one-to-many relationship is automatically created between the table in the Field List pane and the table to which you dragged the field. This relationship, created by Access, does not enforce referential integrity by default. To enforce referential integrity, you must edit the relationship.
See the section Edit a relationship for more information. Open a table in Datasheet view In the Navigation Pane, double-click the table. The Field List pane appears. The Field List pane shows all of the other tables in your database, grouped into categories. When you work with a table in Datasheet view, Access displays fields in either of two categories in the Field List pane: Fields available in related tables and Fields available in other tables.
The first category lists all of the tables that have a relationship with the table with which you are currently working. The second category lists all of the tables with which your table does not have a relationship. To add a field to your table, drag the field that you want from the Field List pane to the table in Datasheet view. Drag the field that you want from the Field List pane to the table that is open in Datasheet view.
When the insertion line appears, drop the field into position. The Lookup Wizard starts. Follow the instructions to complete the Lookup Wizard.
Create a query based on multiple tables
The field appears in the table in Datasheet view. When you drag a field from an "other" unrelated table and then complete the Lookup Wizard, a new one-to-many relationship is automatically created between the table in the Field List and the table to which you dragged the field.
Edit a relationship You change a relationship by selecting it in the Relationships window and then editing it. Carefully position the cursor so that it points to the relationship line, and then click the line to select it.
The relationship line appears thicker when it is selected. With the relationship line selected, double-click it. The Relationships window appears.
If you have not yet defined any relationships and this is the first time you are opening the Relationships window, the Show Table dialog box appears. If the dialog box appears, click Close. On the Design tab, in the Relationships group, click All Relationships. All tables with relationships are displayed, showing relationship lines. Note that hidden tables tables for which the Hidden check box in the table's Properties dialog box is selected and their relationships will not be shown unless Show Hidden Objects is selected in the Navigation Options dialog box.
Click the relationship line for the relationship that you want to change. Select one or more tables, and then click Add. After you have finished adding tables, click Close. Drag a field typically the primary key from one table to the common field the foreign key in the other table.
To drag multiple fields, press the Ctrl key, click each field, and then drag them. The Edit Relationships dialog box appears. Verify that the field names shown are the common fields for the relationship. If a field name is incorrect, click on the field name and select the appropriate field from the list. To enforce referential integrity for this relationship, select the Enforce Referential Integrity box. When you are finished in the Relationships window, click Save to save your relationship layout changes.
Access draws a relationship line between the two tables. If you selected the Enforce Referential Integrity check box, the line appears thicker at each end.
This means that the Indexed property for these fields should be set to Yes No Duplicates. If both fields have a unique index, Access creates a one-to-one relationship. This means that the Indexed property for this field should be set to Yes No Duplicates. In most cases, you drag the primary key field this field is displayed in bold text from one table to a similar field this field frequently has the same name that is called the foreign key in the other table.
Make sure that the field names that are displayed in the two columns are correct. You can change the names if it is necessary. Set the relationship options if it is necessary. These options will be explained in detail later in this article. Click Create to create the relationship. Repeat steps 4 through 7 for each pair of tables that you want to relate. Whether you save the layout or do not save the layout, the relationships that you create are saved in the database.
However, referential integrity is not enforced with queries. How to define a many-to-many relationship To create a many-to-many relationship, follow these steps: Create the two tables that will have a many-to-many relationship.
Create a third table. This is the junction table. In the junction table, add new fields that have the same definitions as the primary key fields from each table that you created in step 1. In the junction table, the primary key fields function as foreign keys. You can add other fields to the junction table, just as you can to any other table.
In the junction table, set the primary key to include the primary key fields from the other two tables.
Create a relationship
Note To create a primary key, follow these steps: Open a table in Design view. Select the field or fields that you want to define as the primary key. To select one field, click the row selector for the desired field. To select multiple fields, hold down the Ctrl key, and then click the row selector for each field. In Access or in Accessclick Primary Key on the toolbar. Define a one-to-many relationship between each primary table and the junction table.
Referential integrity Referential integrity is a system of rules that Access uses to make sure that relationships between records in related tables are valid, and that you do not accidentally delete or change related data. The matching field from the primary table is a primary key or has a unique index.
Create a query based on multiple tables - Access
The related fields have the same data type. There are two exceptions. Both tables belong to the same Access database. If the tables are linked tables, they must be tables in Access format, and you must open the database in which they are stored to set referential integrity. Referential integrity cannot be enforced for linked tables from databases in other formats. The following rules apply when you use referential integrity: You cannot enter a value in the foreign key field of the related table that does not exist in the primary key of the primary table.
However, you can enter a Null value in the foreign key.