How to: Join Tables Manually
When you add two (or more) tables to a query, the Query and View Designer attempts to join them based on common data or on information stored in the database about how tables are related. For details, see How to: Join Tables Automatically. However, if the Query and View Designer has not joined the tables automatically, or if you want to create additional join conditions between tables, you can join tables manually.
You can create joins based on comparisons between any two columns, not just columns that contain the same information. For example, if your database contains two tables, titles and roysched, you can compare values in the ytd_sales column of the titles table against the lorange and hirange columns in the roysched table. Creating this join would allow you to find titles for which the year-to-date sales falls between the low and high ranges for the royalty payments.
Tip
Joins work fastest if the columns in the join condition have been indexed. In some cases, joining on unindexed columns can result in a slow query. For information about creating indexes using the Visual Database Tools, see Working with Indexes.
Note
Your computer might show different names or locations for some of the Visual Studio user interface elements in the following instructions. The Visual Studio edition that you have and the settings that you use determine these elements. For more information, see Customizing Development Settings in Visual Studio.
To manually join tables or table-structured objects
Add to the Diagram pane the objects you want to join.
Drag the name of the join column in the first table or table-structured object and drop it onto the related column in the second table or table-structured object. You cannot base a join on text, ntext, or image columns.
Note
The join columns must be of the same (or compatible) data types. For example, if the join column in the first table is a date, you must relate it to a date column in the second table. On the other hand, if the first join column is an integer, the related join column must also be of an integer data type, but it can be a different size. The Query and View Designer will not check the data types of the columns you use to create a join, but when you execute the query, the database will display an error if the data types are not compatible.
If necessary, change the join operator; by default, the operator is an equal sign (=). For background, see Join Comparison Operators. For details, see How to: Modify Join Operators.
The Query and View Designer adds an INNER JOIN clause to the SQL statement in the SQL pane. You can change the type to an outer join. For details see How to: Create Outer Joins.