Incremental strategies (append, merge, delete+insert) in dbt - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the incremental strategy to append in a dbt model.

dbt

config(materialized='incremental', incremental_strategy='[1]')

Drag options to blanks, or click blank then click option'

Asnapshot

Bappend

Cdelete+insert

Dmerge

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'merge' when only adding rows is needed.

Confusing 'append' with 'delete+insert'.

The append strategy adds new rows without updating existing ones.

2fill in blank

medium

Complete the code to specify the unique key for the merge incremental strategy.

dbt

config(materialized='incremental', incremental_strategy='merge', unique_key='[1]')

Drag options to blanks, or click blank then click option'

Aid

Btimestamp

Cdate

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-unique column as the unique_key.

Leaving unique_key empty for merge strategy.

The unique_key identifies rows to update or insert during a merge.

3fill in blank

hard

Fix the error in the incremental filter condition to only process new data.

dbt

where updated_at > (select max(updated_at) from [1])

Drag options to blanks, or click blank then click option'

Asource_table

Bincremental_table

Ctarget_table

Dstaging_table

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing with the source or staging table instead of the target.

Using a table that does not exist in the context.

The filter should compare with the max timestamp in the target_table to avoid reprocessing old data.

4fill in blank

hard

Fill both blanks to configure a delete+insert incremental strategy with a unique key.

dbt

config(materialized='incremental', incremental_strategy='[1]', unique_key='[2]')

Drag options to blanks, or click blank then click option'

Adelete+insert

Bappend

Cid

Dmerge

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'append' instead of 'delete+insert' for updates.

Not specifying a unique key.

The delete+insert strategy deletes existing rows matching the unique_key before inserting new data.

5fill in blank

hard

Fill all four blanks to write a merge incremental model with unique key and filter for new data.

dbt

config(materialized='incremental', incremental_strategy='[1]', unique_key='[2]')

select * from source_table
where updated_at > (select max([3]) from [4])

Drag options to blanks, or click blank then click option'

Amerge

Bid

Cupdated_at

Dtarget_table

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong incremental strategy.

Not filtering new data correctly.

This code sets the merge strategy with id as the unique key and filters rows where updated_at is newer than the max in the target table.

Practice

1. Which incremental strategy in dbt only adds new rows without modifying existing ones?

easy

A. delete+insert

B. merge

C. append

D. truncate

Solution

1. Step 1: Understand the append strategy

   The append strategy adds only new rows to the existing table without changing any existing data.

2. Step 2: Compare with other strategies

   Merge updates existing rows and adds new ones; delete+insert replaces matching rows; truncate removes all data first.

3. Final Answer:

   append -> Option C

4. Quick Check:

   append = add new rows only [OK]

Hint: Append means add new rows only, no updates [OK]

Common Mistakes:

• Confusing merge with append
• Thinking delete+insert only adds rows
• Assuming truncate is an incremental strategy

2. Which of the following is the correct syntax to define an incremental model using the merge strategy in dbt?

easy

A. config(materialized='incremental', incremental_strategy='append')

B. config(materialized='incremental', strategy='merge')

C. config(materialized='table', incremental_strategy='merge')

D. config(materialized='incremental', incremental_strategy='merge')

Solution

1. Step 1: Identify correct config keys for incremental merge

   dbt requires materialized='incremental' and incremental_strategy='merge' to use merge strategy.

2. Step 2: Check each option for correctness

   config(materialized='incremental', incremental_strategy='append') uses 'append' strategy, not merge; config(materialized='table', incremental_strategy='merge') uses materialized='table' which is not incremental; config(materialized='incremental', strategy='merge') uses wrong key 'strategy'.

3. Final Answer:

   config(materialized='incremental', incremental_strategy='merge') -> Option D

4. Quick Check:

   incremental_strategy='merge' with materialized='incremental' [OK]

Hint: Use incremental_strategy='merge' inside config() for merge [OK]

Common Mistakes:

• Using wrong materialized type
• Misspelling incremental_strategy key
• Confusing strategy key name

3. Given this dbt incremental model snippet using merge strategy:

select id, value from source_table where updated_at > (select max(updated_at) from {{ this }})

What will happen when this model runs?

medium

A. Only new rows with updated_at greater than max in target are added

B. Rows with matching id are updated or inserted based on updated_at filter

C. All rows from source_table replace the target table

D. No rows are added or updated because filter excludes all

Solution

1. Step 1: Understand the filter condition

   The query selects rows from source_table where updated_at is greater than the max updated_at in the target table ({{ this }}).

2. Step 2: Understand merge behavior

   Merge updates existing rows with matching keys and inserts new rows. The filter ensures only changed rows are processed.

3. Final Answer:

   Rows with matching id are updated or inserted based on updated_at filter -> Option B

4. Quick Check:

   merge updates/inserts filtered rows [OK]

Hint: Merge updates or inserts rows filtered by updated_at [OK]

Common Mistakes:

• Thinking it replaces entire table
• Assuming only new rows are appended
• Ignoring the filter condition effect

4. You wrote this incremental model using delete+insert strategy:

config(materialized='incremental', incremental_strategy='delete+insert')

select * from source_table

But the model fails with an error about missing unique key. What is the likely cause?

medium

A. You did not specify the unique_key config required for delete+insert

B. The source_table is empty

C. delete+insert strategy does not support incremental models

D. You must use append strategy instead

Solution

1. Step 1: Recall delete+insert requirements

   Delete+insert requires a unique_key config to identify rows to delete before insert.

2. Step 2: Analyze error cause

   Missing unique_key causes dbt to error because it cannot identify which rows to delete.

3. Final Answer:

   You did not specify the unique_key config required for delete+insert -> Option A

4. Quick Check:

   delete+insert needs unique_key [OK]

Hint: Always set unique_key for delete+insert strategy [OK]

Common Mistakes:

• Ignoring unique_key requirement
• Assuming delete+insert works without keys
• Confusing append with delete+insert

5. You have a large sales table that updates daily with new sales and corrections to existing sales records. Which incremental strategy should you choose in dbt to efficiently update the table without full reloads?

hard

A. merge, because it updates existing rows and adds new ones

B. delete+insert, because it deletes all rows and inserts fresh data

C. append, because it only adds new rows

D. full refresh, because incremental strategies are not suitable

Solution

1. Step 1: Analyze data update needs

   The table has new sales and corrections, so existing rows need updates and new rows need inserts.

2. Step 2: Match strategy to needs

   Append only adds new rows, so it won't update corrections. Delete+insert replaces matching rows but can be costly. Merge efficiently updates and inserts rows incrementally.

3. Final Answer:

   merge, because it updates existing rows and adds new ones -> Option A

4. Quick Check:

   merge = update + insert for corrections and new data [OK]

Hint: Use merge for updates plus new rows efficiently [OK]

Common Mistakes:

• Choosing append and missing updates
• Thinking delete+insert always best
• Ignoring performance of full refresh