How to Keep SQL Server Table Columns in Sync

Introduction

It is possible to come across situations where maintaining column synchronization across two or more tables is necessary while working on SQL Server. It's crucial to make sure that modifications made in one table are reflected in the other, for instance, if you have two tables with User data each, Member and MemberProfiles.

There are several methods that can assist you in achieving this in a reliable and efficient manner. Three of the most popular methods will be covered in this article: using triggers, creating SQL scripts with the INSERT, UPDATE, and DELETE commands, and using the MERGE statement.

1. Using Triggers

Triggers are unique SQL statements that run on their own whenever a table is modified. Triggers can be used to synchronize tables' columns so that changes made in one table are reflected in another. For instance, you might use an AFTER UPDATE trigger to maintain the Name column in the MemberProfiles table and the Members table's Name column in sync.

CREATE TRIGGER trgUpdateMemberProfiles 
ON Members
AFTER UPDATE
AS
BEGIN
    UPDATE MemberProfiles 
    SET Name = u.Name
    FROM MemberProfiles p
    JOIN inserted u ON p.UserId = u.UserId
END;

Whenever the Members table is updated, this trigger is triggered automatically. It synchronizes the changed Name in the Members table with the Name column in the MemberProfiles table using the inserted table, which temporarily stores updated rows. Although this approach is effective for basic synchronization tasks, as the system grows larger, it may become challenging to manage intricate logic using triggers.

2. SQL Scripts 

Writing SQL queries to perform the INSERT, UPDATE, and DELETE actions is a more difficult method of maintaining column consistency between tables. Developers have complete control over the timing and mechanism of synchronization when using this method. You can manually create queries that insert the same data into the MemberProfiles table when you insert a new row into the Members table.

CREATE PROCEDURE AddMemberAndProfile
    @UserId INT,
    @Name NVARCHAR(100),
    @Email NVARCHAR(100),
    @Age INT
AS
BEGIN
    BEGIN TRANSACTION;
    BEGIN TRY   
        INSERT INTO Members(UserId, Name, Email)
        VALUES (@UserId, @Name, @Email);
        INSERT INTO MemberProfiles (UserId, Name, Age)
        VALUES (@UserId, @Name, @Age);
        COMMIT;
    END TRY
    BEGIN CATCH  
        ROLLBACK;
        THROW;
    END CATCH;
END;

The two insertions are handled as a single atomic transaction when BEGIN TRANSACTION is used. To ensure consistency, if one fails, the other gets rolled back. This method gives you flexibility and control, but it also necessitates writing and updating manual queries, which can get difficult as your application gets bigger.

3. Using the MERGE Statement (Best for Automation)

An effective method for automating table synchronization is the MERGE statement. It's a great option for quickly and easily maintaining table synchronization because it integrates INSERT, UPDATE, and DELETE actions into a single query. A row is checked to see if it already exists in both tables-> if it does-> it is updated. If not then its inserted.

MERGE INTO MemberProfiles AS Target
USING (SELECT UserId, Name FROM Members) AS Source
ON Target.UserId = Source.UserId
WHEN MATCHED THEN
    UPDATE SET Target.Name = Source.Name
WHEN NOT MATCHED BY TARGET THEN
    INSERT (UserId, Name)
    VALUES (Source.UserId, Source.Name);

Here, the MemberProfiles table is the Target and the Members table is the Source. The Name column in the MemberProfiles table is updated if a matching UserId is discovered. A new row is introduced if no match is discovered. Because it eliminates the need to write several queries, this solution is perfect for developers searching for a simplified, automated approach to data synchronization.

Which Method Should You Apply?

Triggers: Ideal for basic synchronization if you want the second table to automatically maintain synchronization at all times.
SQL Scripts: Excellent if you want complete control over the timing and method of data synchronization, but they involve more manual effort.
MERGE Statement: The most effective way to handle complex situations with a single, clear query and automate the procedure.

Conclusion

Data consistency requires that columns in SQL Server tables be consistent. Every approach has its own benefits, whether it is using the potent MERGE command for efficiency, manual SQL scripts for control, or triggers for automation. Select the method that assures reliable synchronization and best suits the requirements of your application.