Lesson Contribution - Lesson Order

[Talishask]

I'm a member of The Carpentries Core Team and I'm submitting this issue on behalf of another member of the community. In most cases, I won't be able to follow up or provide more details other than what I'm providing below.

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The concept of NULLs is introduced in the "Aggregating & Grouping Data" episode. I suggest moving the "Functions COALESCE & NULLIF and more" section from the "Combining Data with Joins" episode into a new one perhaps called "NULL and SQL Functions". Covering the functions dealing with NULLs right after the introduction of the concept makes more sense as it flows better. The current order might confuse learners in thinking that you can use those functions only in JOINS. When in fact functions in general are useful in both simple and complex queries. Also, to ensure an equal content distribution, move "Aliases" & "What About Null?" into the new episode.

CURRENT LESSON ORDER:

1. Introducing Databases and SQL
2. Accessing Data with Queries
3. Aggregating and Grouping Data

• COUNT and GROUP BY
• Ordering Aggregated Results
• Aliases
• The HAVING keyword
• Saving Queries for Future Use
• What About NULL?

4. Combining Data with Joins

• Joins
• Different join types
• Combining joins with sorting and aggregation
• Functions COALESCE and NULLIF and more

SUGGESTED LESSON ORDER:

1. Introducing Databases and SQL
2. Accessing Data with Queries
3. Aggregating and Grouping Data

• COUNT and GROUP BY
• Ordering Aggregated Results
• The HAVING keyword
• Saving Queries for Future Use

4. NULL and SQL Functions

• What About NULL?
• Functions COALESCE and NULLIF
• Other Functions
• Aliases

5. Combining Data with Joins

• Joins
• Different join types
• Combining joins with sorting and aggregation