Hi, I'm Tom Blessing. I'm an expert at helping small to mid-sized companies adopt Power BI. I'm also a recovering investment banker, with deep experience applying technology to otherwise manual data problems. I have dual degrees in Finance and Technology Management from Indiana University.

Merging tables in Power Query should feel like a breeze.

But sometimes, it feels more like you're stuck in quicksand.

Don't fret! Here are some tips to accelerate the process. 

Understand the Basics

Power Query, while powerful, can slow down with large datasets or complex merges. Being aware helps set expectations. 

Filter Before You Merge

Reduce your tables to essential data before merging. Fewer rows mean faster merge times. 

Indexing for the Win

Just like databases, creating indexes can speed up merging. Especially true if you're merging on non-numeric columns. 

Reduce Column Count

Don't just focus on rows. Limiting columns, especially unnecessary ones, can significantly boost speed. 

Check Data Types

Ensure consistency in data types you're merging on. Mismatched types can cause slowdowns. 

Avoid Using "Full Outer" Joins

"Full Outer" joins, while comprehensive, are resource-intensive. If possible, opt for "Inner" or "Left Outer" joins. 

Limit Nested Queries

Nested queries can be a performance nightmare. Try to flatten queries and make them more linear. 

Monitor Background Data

While merging, Power Query fetches data in the background. Turn off background data in 'Options' to potentially speed things up. 

Upgrade Hardware

While optimizing queries is great, sometimes the issue is hardware. Consider more RAM or an SSD upgrade. 

Update Power BI Desktop

Always run the latest version. Updates often come with performance enhancements. 

Be Wary of Custom Functions

Custom functions, while flexible, can slow things down. Use built-in functions when possible. 

Seek Feedback

The Power BI Community is vibrant. Post your query details and get insights from experts who might spot optimization opportunities.

Conclusion:

Merging tables in Power Query can test your patience when it slows down.

But with these tweaks and optimizations, you can streamline the process.

Remember, it's not just about making it faster, but also about making it smarter.

Happy merging!