Tom Mitchell
@imtommitchell.bsky.social
I help ambitious professionals develop high paying data skills | Cloud Data Engineer & Analytics Consultant (8+ YOE) | Ex-Data @ Revolut
I hope you've found this thread helpful.
If you did, I ask for 2 small favours:
1. Follow me @imtommitchell for more like this daily.
2. Click below, jump to the top and share to help someone else.
If you did, I ask for 2 small favours:
1. Follow me @imtommitchell for more like this daily.
2. Click below, jump to the top and share to help someone else.
August 23, 2025 at 8:57 AM
I hope you've found this thread helpful.
If you did, I ask for 2 small favours:
1. Follow me @imtommitchell for more like this daily.
2. Click below, jump to the top and share to help someone else.
If you did, I ask for 2 small favours:
1. Follow me @imtommitchell for more like this daily.
2. Click below, jump to the top and share to help someone else.
3 months from now, you could be:
– Building data solutions that matter
– The "go-to" person in your business for data
– Being considered for jobs you wouldn't have before
– Building data solutions that matter
– The "go-to" person in your business for data
– Being considered for jobs you wouldn't have before
August 23, 2025 at 8:57 AM
3 months from now, you could be:
– Building data solutions that matter
– The "go-to" person in your business for data
– Being considered for jobs you wouldn't have before
– Building data solutions that matter
– The "go-to" person in your business for data
– Being considered for jobs you wouldn't have before
Don't wait.
Get started today:
Go to portal.azure.com
Claim your free £150 credit
Start with Azure Data Factory fundamentals
Get started today:
Go to portal.azure.com
Claim your free £150 credit
Start with Azure Data Factory fundamentals
August 23, 2025 at 8:57 AM
Don't wait.
Get started today:
Go to portal.azure.com
Claim your free £150 credit
Start with Azure Data Factory fundamentals
Get started today:
Go to portal.azure.com
Claim your free £150 credit
Start with Azure Data Factory fundamentals
Data engineering isn't about being a coding genius.
It's about being a problem-solving translator.
You take business questions and find the data answers.
It's about being a problem-solving translator.
You take business questions and find the data answers.
August 23, 2025 at 8:57 AM
Data engineering isn't about being a coding genius.
It's about being a problem-solving translator.
You take business questions and find the data answers.
It's about being a problem-solving translator.
You take business questions and find the data answers.
4. Automation
- Schedule data pipelines.
- Set up monitoring and alerts.
- Build something a client would pay for.
- Schedule data pipelines.
- Set up monitoring and alerts.
- Build something a client would pay for.
August 23, 2025 at 8:57 AM
4. Automation
- Schedule data pipelines.
- Set up monitoring and alerts.
- Build something a client would pay for.
- Schedule data pipelines.
- Set up monitoring and alerts.
- Build something a client would pay for.
3. Analytics & Visualisation
- Explore Azure Synapse Analytics.
- Create dashboards in Power BI.
- Turn messy data into clear insights.
- Explore Azure Synapse Analytics.
- Create dashboards in Power BI.
- Turn messy data into clear insights.
August 23, 2025 at 8:57 AM
3. Analytics & Visualisation
- Explore Azure Synapse Analytics.
- Create dashboards in Power BI.
- Turn messy data into clear insights.
- Explore Azure Synapse Analytics.
- Create dashboards in Power BI.
- Turn messy data into clear insights.
2. Storage & Processing
- Master Azure Data Lake.
- Understand data warehousing basics.
- Connect to real business databases.
- Master Azure Data Lake.
- Understand data warehousing basics.
- Connect to real business databases.
August 23, 2025 at 8:57 AM
2. Storage & Processing
- Master Azure Data Lake.
- Understand data warehousing basics.
- Connect to real business databases.
- Master Azure Data Lake.
- Understand data warehousing basics.
- Connect to real business databases.
1. Foundation
Set up your free account. You get £150 credit included.
- Set up Azure Data Factory.
- Learn to move data between systems.
- Build your first data pipeline.
Set up your free account. You get £150 credit included.
- Set up Azure Data Factory.
- Learn to move data between systems.
- Build your first data pipeline.
August 23, 2025 at 8:57 AM
1. Foundation
Set up your free account. You get £150 credit included.
- Set up Azure Data Factory.
- Learn to move data between systems.
- Build your first data pipeline.
Set up your free account. You get £150 credit included.
- Set up Azure Data Factory.
- Learn to move data between systems.
- Build your first data pipeline.
If you liked this post, you'll love my weekly newsletter.
I share everything I know about building high-paying data skills from my 8+ years in the industry.
Subscribe for free here:
thedatadose.com
I share everything I know about building high-paying data skills from my 8+ years in the industry.
Subscribe for free here:
thedatadose.com
August 22, 2025 at 8:59 AM
If you liked this post, you'll love my weekly newsletter.
I share everything I know about building high-paying data skills from my 8+ years in the industry.
Subscribe for free here:
thedatadose.com
I share everything I know about building high-paying data skills from my 8+ years in the industry.
Subscribe for free here:
thedatadose.com
7. That's it!
TL;DR:
- Index your large tables
- Be specific with SELECT statements
- Use EXISTS instead of COUNT
- Optimise your JOINs
- Filter early and often
TL;DR:
- Index your large tables
- Be specific with SELECT statements
- Use EXISTS instead of COUNT
- Optimise your JOINs
- Filter early and often
August 22, 2025 at 8:59 AM
7. That's it!
TL;DR:
- Index your large tables
- Be specific with SELECT statements
- Use EXISTS instead of COUNT
- Optimise your JOINs
- Filter early and often
TL;DR:
- Index your large tables
- Be specific with SELECT statements
- Use EXISTS instead of COUNT
- Optimise your JOINs
- Filter early and often
6. Bonus tip
Most databases have a query optimizer that chooses the best execution plan.
But it can only work with what you give it.
Write efficient queries and the optimiser will take them to the next level.
Most databases have a query optimizer that chooses the best execution plan.
But it can only work with what you give it.
Write efficient queries and the optimiser will take them to the next level.
August 22, 2025 at 8:59 AM
6. Bonus tip
Most databases have a query optimizer that chooses the best execution plan.
But it can only work with what you give it.
Write efficient queries and the optimiser will take them to the next level.
Most databases have a query optimizer that chooses the best execution plan.
But it can only work with what you give it.
Write efficient queries and the optimiser will take them to the next level.
5. Filter early and often
Put your WHERE clause before HAVING.
Use LIMIT to sample results during development.
Avoid != and <> operators when possible.
Filter your data as early as possible in the query process.
Put your WHERE clause before HAVING.
Use LIMIT to sample results during development.
Avoid != and <> operators when possible.
Filter your data as early as possible in the query process.
August 22, 2025 at 8:59 AM
5. Filter early and often
Put your WHERE clause before HAVING.
Use LIMIT to sample results during development.
Avoid != and <> operators when possible.
Filter your data as early as possible in the query process.
Put your WHERE clause before HAVING.
Use LIMIT to sample results during development.
Avoid != and <> operators when possible.
Filter your data as early as possible in the query process.
4. Optimise your JOINs
Use INNER JOIN syntax, not WHERE clauses for joins.
The query optimiser handles INNER JOINs much better.
Also: Use UNION ALL instead of UNION when you don't need to remove duplicates.
Use INNER JOIN syntax, not WHERE clauses for joins.
The query optimiser handles INNER JOINs much better.
Also: Use UNION ALL instead of UNION when you don't need to remove duplicates.
August 22, 2025 at 8:59 AM
4. Optimise your JOINs
Use INNER JOIN syntax, not WHERE clauses for joins.
The query optimiser handles INNER JOINs much better.
Also: Use UNION ALL instead of UNION when you don't need to remove duplicates.
Use INNER JOIN syntax, not WHERE clauses for joins.
The query optimiser handles INNER JOINs much better.
Also: Use UNION ALL instead of UNION when you don't need to remove duplicates.
3. Use EXISTS instead of COUNT
When checking if records exist, use EXISTS() instead of COUNT().
COUNT scans the entire result set.
EXISTS stops at the first match.
Massive difference in performance.
When checking if records exist, use EXISTS() instead of COUNT().
COUNT scans the entire result set.
EXISTS stops at the first match.
Massive difference in performance.
August 22, 2025 at 8:59 AM
3. Use EXISTS instead of COUNT
When checking if records exist, use EXISTS() instead of COUNT().
COUNT scans the entire result set.
EXISTS stops at the first match.
Massive difference in performance.
When checking if records exist, use EXISTS() instead of COUNT().
COUNT scans the entire result set.
EXISTS stops at the first match.
Massive difference in performance.
2. Be specific with SELECT statements
Stop using SELECT *.
It's lazy. It's slow. It's unprofessional.
Only select the columns you actually need.
This single change can cut query time by 70%.
Stop using SELECT *.
It's lazy. It's slow. It's unprofessional.
Only select the columns you actually need.
This single change can cut query time by 70%.
August 22, 2025 at 8:59 AM
2. Be specific with SELECT statements
Stop using SELECT *.
It's lazy. It's slow. It's unprofessional.
Only select the columns you actually need.
This single change can cut query time by 70%.
Stop using SELECT *.
It's lazy. It's slow. It's unprofessional.
Only select the columns you actually need.
This single change can cut query time by 70%.
1. Index your large tables
If your table has more than 1 million rows and you're not using indexes, you're doing it wrong.
Create indexes on columns you frequently query.
Your database (and other devs) will thank you.
If your table has more than 1 million rows and you're not using indexes, you're doing it wrong.
Create indexes on columns you frequently query.
Your database (and other devs) will thank you.
August 22, 2025 at 8:59 AM
1. Index your large tables
If your table has more than 1 million rows and you're not using indexes, you're doing it wrong.
Create indexes on columns you frequently query.
Your database (and other devs) will thank you.
If your table has more than 1 million rows and you're not using indexes, you're doing it wrong.
Create indexes on columns you frequently query.
Your database (and other devs) will thank you.