Скачать или смотреть Count the Number of Identical Values in Different SQL Columns

Learn how to count identical values across different columns in SQL, using either the `CROSS APPLY` or `UNPIVOT` methods.
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Counting Identical Values in Different SQL Columns

When working with SQL databases, you may encounter situations where you need to tally identical values present in different columns of a table. This can be particularly useful in data analysis, reporting, and database management tasks. In this guide, we will explore how to count these identical values effectively, breaking down the solution into two main approaches: using the CROSS APPLY and UNPIVOT functions.

The Problem

Consider a scenario where you have a table containing several columns with integer values, and you want to know how many times each value appears across specified columns. For example, given the following table structure:

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

The goal is to produce a result that counts occurrences of each unique value from Field_A, Field_B, Field_C, and Field_D. Your desired output might look like this:

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

The Solution

Using CROSS APPLY

One way to achieve this result is by utilizing the CROSS APPLY function. This powerful SQL feature allows you to join each row in your main table with values in the specified columns.

Step 1: Set Up the Table
First, create and insert the data into a temporary table:

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

Step 2: Execute the Query with CROSS APPLY
Next, perform the count using CROSS APPLY:

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

This query will provide a count of each value in the different fields.

Alternative Approach: Using UNPIVOT

Another effective method for counting identical values is using the UNPIVOT function. This approach can simplify the process by transforming columns into rows.

Step 1: Execute the Query with UNPIVOT
Using the same table structure from before, you can apply UNPIVOT as follows:

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

This query will yield the number of occurrences of each value across the specified columns.

Conclusion

Counting identical values across different columns in SQL is a common requirement that can be accomplished in multiple ways. Whether you choose the CROSS APPLY approach for more flexibility or the UNPIVOT method for simplicity and directness depends on your specific use case and familiarity with SQL functions. Both strategies will help provide valuable insights into your data.

By implementing these SQL techniques, you'll be able to derive meaningful information from your data more efficiently. Feel free to experiment with the codes provided to see how they perform with your datasets!