Querying and Comparing Remote Databases in Access

Introduction to Querying and Comparing Remote Databases in Access

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As an Access user, you’ve likely encountered the need to compare data between multiple databases, especially when working with remote access databases. In this article, we’ll explore how to query and compare these remote databases using Access’s built-in features.

Understanding Linked and Remote Databases

Before diving into querying and comparing remote databases, it’s essential to understand the difference between linked and remote databases.

Linked Databases: These are databases that are connected directly to each other via a link. When you open a database file from a linked database, Access creates a connection to the original database.
Remote Databases: These are databases located on another computer or network. You can access these databases using their path or network location.

Querying and comparing remote databases requires additional steps compared to linking them. In this article, we’ll focus on querying and comparing remote databases in Access.

Querying Remote Databases

To query a remote database, you need to use the SELECT statement followed by IN and the path to the database file.

SELECT * FROM DGConcept IN 'C:\Users\Gusto\Desktop\A.accdb'

This syntax tells Access to select all records from the DGConcept table in the specified database file.

Creating a Query for Remote Databases

To create a query that queries both remote databases, you can use the following syntax:

SELECT *
FROM (SELECT * FROM DGConcept IN 'C:\Users\Gusto\Desktop\A.accdb') x
LEFT JOIN (SELECT * FROM DGConcept IN 'C:\Users\Gusto\Desktop\B.accdb') y
ON (x.[ID] = y.[ID])
WHERE ((y.ID) Is Null)

This query creates two subqueries that select records from both remote databases. The LEFT JOIN clause combines the results of these subqueries, matching records based on the [ID] column.

Handling NULL Values

To find differences between the two tables, you need to handle NULL values. You can do this by adding a WHERE clause that selects only rows where the y.ID is NULL:

SELECT *
FROM (SELECT * FROM DGConcept IN 'C:\Users\Gusto\Desktop\A.accdb') x
LEFT JOIN (SELECT * FROM DGConcept IN 'C:\Users\Gusto\Desktop\B.accdb') y
ON (x.[ID] = y.[ID])
WHERE ((y.ID) Is Null)

However, this approach has limitations. To find all differences between the two tables, you need to use UNION ALL with another query:

SELECT 'New in A file', X.*
FROM (SELECT * FROM DGConcept IN 'C:\Users\Gusto\Desktop\A.accdb') x
LEFT JOIN (SELECT * FROM DGConcept IN 'C:\Users\Gusto\Desktop\B.accdb') y
ON (x.[ID] = y.[ID])
WHERE ((y.ID) Is Null)

UNION ALL

SELECT 'New in B file', X.*
FROM (SELECT * FROM DGConcept IN 'C:\Users\Gusto\Desktop\B.accdb') x
LEFT JOIN (SELECT * FROM DGConcept IN 'C:\Users\Gusto\Desktop\A.accdb') y
ON (x.[ID] = y.[ID])
WHERE ((y.ID) Is Null)

This query uses UNION ALL to combine the results of two queries: one that finds records only in database A, and another that finds records only in database B.

Creating a View for Remote Databases

To create a view that combines the results of both remote databases, you can use the following syntax:

CREATE VIEW CombinedView AS

SELECT 'New in A file', x.*
FROM (SELECT * FROM DGConcept IN 'C:\Users\Gusto\Desktop\A.accdb') x
LEFT JOIN (SELECT * FROM DGConcept IN 'C:\Users\Gusto\Desktop\B.accdb') y
ON (x.[ID] = y.[ID])
WHERE ((y.ID) Is Null)

UNION ALL

SELECT 'New in B file', x.*
FROM (SELECT * FROM DGConcept IN 'C:\Users\Gusto\Desktop\B.accdb') x
LEFT JOIN (SELECT * FROM DGConcept IN 'C:\Users\Gusto\Desktop\A.accdb') y
ON (x.[ID] = y.[ID])
WHERE ((y.ID) Is Null)

This view combines the results of both queries, making it easier to compare data between remote databases.

Conclusion

Querying and comparing remote databases in Access requires additional steps compared to linking them. By using SELECT, IN, LEFT JOIN, and UNION ALL clauses, you can query and compare remote databases effectively. Additionally, creating a view that combines the results of both remote databases makes it easier to analyze data.

Remember to handle NULL values correctly when querying and comparing remote databases. With these techniques, you’ll be able to efficiently work with remote databases in Access.

Example Use Case:

Suppose you have two remote databases: Database A and Database B. You want to create a view that combines the records from both databases, excluding any duplicates.

CREATE VIEW CombinedView AS

SELECT 'New in A file', x.*
FROM (SELECT * FROM DGConcept IN 'C:\Users\Gusto\Desktop\A.accdb') x
LEFT JOIN (SELECT * FROM DGConcept IN 'C:\Users\Gusto\Desktop\B.accdb') y
ON (x.[ID] = y.[ID])
WHERE ((y.ID) Is Null)

UNION ALL

SELECT 'New in B file', x.*
FROM (SELECT * FROM DGConcept IN 'C:\Users\Gusto\Desktop\B.accdb') x
LEFT JOIN (SELECT * FROM DGConcept IN 'C:\Users\Gusto\Desktop\A.accdb') y
ON (x.[ID] = y.[ID])
WHERE ((y.ID) Is Null)

EXCEPT

SELECT *
FROM CombinedView
WHERE ([Name] IS NOT NULL)

This view combines the records from both remote databases, excluding any duplicates.

Tips and Variations:

To query a specific table or range of tables, modify the SELECT statement to include only those columns or tables.
To use other aggregate functions, such as SUM, AVG, or MAX, add them to the SELECT statement.
To group results by a specific column, use the GROUP BY clause.

By following these techniques and tips, you’ll be able to efficiently query and compare remote databases in Access.

Last modified on 2023-11-02