92. Joining tables together with INNER JOIN

To calculate ROI for a specific marketing campaign we need to know 2 numbers:

  • total spend. We’d need to apply grouping and summing in marketing_spends table
  • total earnings. We’d need to look at users who were attributed to this campaign and calculate the sum of their purchases. Wow, that’s even more tricky – users and purchases are 2 different tables 🙀

The solution to this problem ☝ and many more data problems is joining two or more tables.

Joining tables is basically forming a new table which is the combination of two or more tables. Once...

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