Cloud Spanner Interleaved Tables: Cascade Delete Behavior
Exhibit
CREATE TABLE Customers ( CustomerId INT64 NOT NULL, Name STRING(1024), ) PRIMARY KEY (CustomerId); CREATE TABLE Orders ( CustomerId INT64 NOT NULL, OrderId INT64 NOT NULL, OrderDate DATE, ) PRIMARY KEY (CustomerId, OrderId), INTERLEAVE IN PARENT Customers ON DELETE CASCADE;
Refer to the exhibit. A company creates these Cloud Spanner tables. What happens when a customer record is deleted?
Quick Answer
The answer is that all orders for that customer are automatically deleted. This occurs because Cloud Spanner interleaved tables enforce parent-child referential integrity at the storage level, meaning child rows are physically stored with their parent row. When a parent row in the Customers table is deleted, the database engine automatically performs a cascade delete on all interleaved child rows in the Orders table, without requiring an explicit ON DELETE CASCADE clause. On the Google Professional Cloud Database Engineer exam, this concept tests your understanding of how interleaving differs from traditional foreign key constraints—a common trap is assuming you need to manually script cascading deletes or that interleaving only affects query performance. Remember that interleaving is both a storage and integrity mechanism: the parent row owns its children, so deleting the parent removes the entire family. A useful memory tip is to think of interleaved tables as nested folders—deleting the folder deletes everything inside it.
⚠ Common exam trap
Many candidates assume Cloud Spanner behaves like traditional relational databases (e.g., requiring explicit ON DELETE CASCADE or failing on foreign key violations), but interleaved tables automatically cascade deletes without any additional syntax.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
All orders for that customer are automatically deleted.
Cloud Spanner enforces referential integrity through interleaved tables. When a parent row in the Customers table is deleted, all child rows in the Orders table that are interleaved under that customer are automatically deleted via a cascading delete. This behavior is inherent to the interleaved table structure, not an explicit ON DELETE CASCADE clause.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The deletion fails if there are orders.
Why it's wrong here
ON DELETE CASCADE allows deletion without failure; it cascades to child rows.
- ✗
The orders are deleted only if the order date is older than 30 days.
Why it's wrong here
Cascade deletes all child rows regardless of age; there is no condition.
- ✓
All orders for that customer are automatically deleted.
Why this is correct
Cascade delete removes all child rows associated with the deleted parent row.
- ✗
The orders remain orphaned.
Why it's wrong here
Orphaned rows are not left; they are deleted due to CASCADE.
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Same concept, more angles
1 more way this is tested on PCDE
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company has a parent-child relationship in Cloud Spanner. They want to minimize cross-table join latency. What should they use?
medium- ✓ A.Interleaved tables
- B.Cloud Functions
- C.Stored procedures
- D.Secondary indexes
JA
Written by Johnson Ajibi, MSc IT Security
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