Скачать или смотреть How to Compare Dynamic Column Headers in SQL

Learn how to effectively compare dynamic column headers from a source file with static columns in SQL using T-SQL. Identify missing columns with ease!
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This video is based on the question https://stackoverflow.com/q/72215785/ asked by the user 'Beanymattd' ( https://stackoverflow.com/u/9052018/ ) and on the answer https://stackoverflow.com/a/72217192/ provided by the user 'crammers' ( https://stackoverflow.com/u/4593739/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Introduction

When working with data in SQL Server, you may encounter scenarios where you need to dynamically manage and compare column headers from different tables. For instance, in a situation where you're importing a file using SQL Server Integration Services (SSIS), you may import dynamic column headers into a staging table (let's call it Table 1) and then need to compare these headers with static columns in another table (let's call this Table 2).

This post provides a detailed solution for highlighting any dynamic column headers in Table 1 that are not present in Table 2.

The Problem Explained

Imagine you have two tables where:

Table 1 has dynamic columns imported from a source file, like so:

Column 1Column 2CustomerIDCustomerNameTable 2 has static columns defined explicitly, such as:

CustomerIDCustomerName1Joe2DanielIf new columns, like CustomerLocation, are added to Table 1, you need a way to compare it to Table 2 and highlight any columns that are missing.

The Solution

To accomplish this task, we can leverage T-SQL and the sys.columns system view to retrieve static column headers from Table 2 and compare them with the headers in Table 1. Here’s how to do it step by step:

Step 1: Initialize Temporary Tables

We will first create temporary tables to hold the column names from both tables.

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Insert Dynamic Columns from Table 1

Next, we can use the UNPIVOT function to extract the dynamic column names from the first row of Table 1.

[[See Video to Reveal this Text or Code Snippet]]

Note: Ensure that you modify the above selection to match your actual column structure and data.

Step 3: Insert Static Columns from Table 2

Now, fetch the static column names from Table 2 using the sys.columns view.

[[See Video to Reveal this Text or Code Snippet]]

Step 4: Compare the Two Tables

Finally, execute a full outer join to compare the two sets of column names.

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

With this approach, you can effectively compare dynamic column headers with static columns in SQL Server. By using T-SQL and leveraging the built-in system views, you can easily identify any discrepancies between your imported data and the expected schema.

Feel free to modify the final selection query to return exactly what you need based on your application requirements. This method not only highlights missing columns but also sets a solid groundwork for handling dynamic schema changes in your SQL workflows.

If you have any questions or need further assistance, don't hesitate to reach out in the comments below!