Access relationship between two tables

access relationship between two tables

relationships between your tables so that Access can bring related . No two records can have the same value in the primary key field or combination of fields. Describes how to define relationships in a database in Access , Access , Access , Access , or Access In the Relationships window, add the Items table twice. The second occurence will automatically get an alias. Use the 2 occurences like if they.

Create a table relationship by using the Relationships window On the Database Tools tab, in the Relationships group, click Relationships. The Relationships window is not available in an Access web app. To create a relationship in an Access web app, see the steps in Create a relationship.

access relationship between two tables

If you have not yet defined any relationships, the Show Table dialog box automatically appears. If it does not appear, on the Design tab, in the Relationships group, click Show Table. The Show Table dialog box displays all of the tables and queries in the database. To see only tables, click Tables.

To see only queries, click Queries. To see both, click Both. Select one or more tables or queries and then click Add. After you have finished adding tables and queries to the Relationships document tab, 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 check box. For more information about referential integrity, see the section Enforce Referential Integrity.

Create a relationship - Access

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.

The field on the many side should not have a unique index. It can have an index, but it must allow duplicates. When one field has a unique index, and the other does not, Access creates a one-to-many relationship.

Top of Page Create a table relationship by using the Field List pane to add a field You can add a field to an existing table that is open in Datasheet view by dragging it from the Field List pane. 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.

access relationship between two tables

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.

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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. 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.

access relationship between two tables

The foreign key side of a relationship is denoted by an infinity symbol. Many-to-many relationships In a many-to-many relationship, a row in table A can have many matching rows in table B, and vice versa. You create such a relationship by defining a third table that is called a junction table. The primary key of the junction table consists of the foreign keys from both table A and table B.

For example, the "Authors" table and the "Titles" table have a many-to-many relationship that is defined by a one-to-many relationship from each of these tables to the "TitleAuthors" table.

One-to-one relationships In a one-to-one relationship, a row in table A can have no more than one matching row in table B, and vice versa. A one-to-one relationship is created if both of the related columns are primary keys or have unique constraints. This kind of relationship is not common, because most information that is related in this manner would be in one table.

You might use a one-to-one relationship to take the following actions: Divide a table with many columns. Isolate part of a table for security reasons. Store data that is short-lived and could be easily deleted by deleting the table. Store information that applies only to a subset of the main table. In Access, the primary key side of a one-to-one relationship is denoted by a key symbol.

The foreign key side is also denoted by a key symbol. How to define relationships between tables When you create a relationship between tables, the related fields do not have to have the same names. However, related fields must have the same data type unless the primary key field is an AutoNumber field. You can match an AutoNumber field with a Number field only if the FieldSize property of both of the matching fields is the same.

access relationship between two tables

Even when both matching fields are Number fields, they must have the same FieldSize property setting. How to define a one-to-many or one-to-one relationship To create a one-to-many or a one-to-one relationship, follow these steps: You cannot create or change relationships between open tables. In Access or Accessfollow these steps: Press F11 to switch to the Database window. On the Tools menu, click Relationships. If you have not yet defined any relationships in your database, the Show Table dialog box is automatically displayed.

To create a relationship between a table and itself, add that table two times. Drag the field that you want to relate from one table to the related field in the other table. To drag multiple fields, press Ctrl, click each field, and then drag them. 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.

Create, edit or delete a relationship - Access

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. 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.

Creating a Relationship between two Tables in an Access Database

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.