How to save combine table in PBI without loading again when re-opening PBI file

Hi, nminh_phuong 

It sounds like your issue arises from Power BI having to process large CSV files every time you open your file. A potential solution to this problem could be to utilize Power BI's incremental refresh feature.

Incremental refresh allows Power BI to only load new or changed data from the source. This can significantly reduce the amount of time it takes to load data, especially for large files, as in your case.

However, there's a catch. Incremental refresh is not available for flat files like CSV out of the box. It's primarily used with SQL databases. But there's a workaround you could try:

1. Load the CSV files into a database: If you have access to a SQL Server database, you could import your CSV files into a SQL Server table. This could be done using SQL Server's import wizard, SSIS, or any other ETL tool that you have access to.

2. Set up an incremental refresh policy: Once you have the data in SQL Server, you can set up an incremental refresh policy in Power BI. When setting up the policy, you would need to specify a "filter" column. This could be a date column, for example, which would allow Power BI to load only new or changed data based on the date.

3. Connect to the SQL Server data source in Power BI: Instead of connecting to the CSV files directly, you would now connect to the SQL Server data source. Power BI would then use the incremental refresh policy to load the data, which should be much faster.
   
   Alternatively, you can make fair use of Power BI dataflow. Pull the data in a dataflow, transform it there, and then from your Power BI desktop connect to Dataflow to load your data. 
   
   If Power BI DF and SQL server is not an option then you use DirectQuery instead of import. This could reduce the loading time. 

Keep in mind that this is a bit of a workaround, and it would require having access to a SQL Server or similar database, and the ability to load the data into it.

In terms of the "Combine table" not keeping the same format and value, you might want to look at the steps in your query where you're transforming the data. You might need to adjust these steps to ensure that the transformations are consistent across different data loads. If the data in the CSV files is changing, you might also need to adjust the transformations to account for these changes.

Also, remember that Power BI stores data in a compressed, in-memory format. This means that when you load data into Power BI, it gets stored in the file itself. So, while the initial load of the data may take some time, once the data is loaded, you should be able to work with it quickly, even if the original data source was a large file.

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