Database triggers for automation in Supabase - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a trigger that runs after an insert on the 'orders' table.

Supabase

CREATE TRIGGER order_insert_trigger AFTER [1] ON orders FOR EACH ROW EXECUTE FUNCTION notify_order();

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

AUPDATE

BDELETE

CINSERT

DTRUNCATE

Attempts:

3 left

💡 Hint

Common Mistakes

Using UPDATE instead of INSERT

Using DELETE which triggers on row removal

Using TRUNCATE which is not supported for triggers

The trigger should run after an INSERT event on the 'orders' table to automate actions when new orders are added.

2fill in blank

medium

Complete the code to define a trigger function that logs the new row's id after insert.

Supabase

CREATE FUNCTION log_new_order() RETURNS trigger AS $$ BEGIN INSERT INTO order_logs(order_id) VALUES (NEW.[1]); RETURN NEW; END; $$ LANGUAGE plpgsql;

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

Aid

Buser_id

Ccreated_at

Dstatus

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-primary key field like 'user_id'

Using 'created_at' which is a timestamp

Using 'status' which is unrelated to the id

The NEW keyword refers to the new row inserted. To log the order, we use its id field.

3fill in blank

hard

Fix the error in the trigger creation by completing the missing keyword.

Supabase

CREATE TRIGGER update_status_trigger BEFORE UPDATE ON orders FOR EACH ROW [1] FUNCTION update_status();

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

ASTART

BRUN

CCALL

DEXECUTE

Attempts:

3 left

💡 Hint

Common Mistakes

Using RUN instead of EXECUTE

Using CALL which is not valid for triggers

Omitting the keyword entirely

The correct keyword to link a trigger to a function is EXECUTE FUNCTION.

4fill in blank

hard

Fill both blanks to create a trigger that fires after delete and calls the cleanup function.

Supabase

CREATE TRIGGER cleanup_trigger AFTER [1] ON sessions FOR EACH ROW [2] FUNCTION cleanup_session();

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

ADELETE

BINSERT

CEXECUTE

DUPDATE

Attempts:

3 left

💡 Hint

Common Mistakes

Using INSERT or UPDATE instead of DELETE

Using CALL or RUN instead of EXECUTE

The trigger should fire after a DELETE event and use the keyword EXECUTE to call the function.

5fill in blank

hard

Fill all three blanks to create a trigger that updates the 'updated_at' timestamp before any update on the 'profiles' table.

Supabase

CREATE TRIGGER update_timestamp BEFORE [1] ON profiles FOR EACH ROW [2] FUNCTION [3]();

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

AUPDATE

BEXECUTE

Cset_updated_at

DINSERT

Attempts:

3 left

💡 Hint

Common Mistakes

Using INSERT instead of UPDATE

Using CALL or RUN instead of EXECUTE

Using wrong function names

The trigger fires BEFORE UPDATE, uses EXECUTE FUNCTION, and calls the function set_updated_at to update the timestamp.

Practice

1. What is the main purpose of a database trigger in Supabase?

easy

A. To manually update data in the database

B. To automatically run a function when data changes in a table

C. To create a backup of the database

D. To increase the database storage size

Solution

1. Step 1: Understand what triggers do

   Triggers run automatically when data changes like insert, update, or delete.

2. Step 2: Identify the purpose in Supabase

   Supabase triggers automate running functions on data changes without manual intervention.

3. Final Answer:

   To automatically run a function when data changes in a table -> Option B

4. Quick Check:

   Trigger = auto-run function on data change [OK]

Hint: Triggers run code automatically on data changes [OK]

Common Mistakes:

• Thinking triggers require manual activation
• Confusing triggers with backups
• Assuming triggers increase storage

2. Which of the following is the correct syntax to create a trigger in Supabase SQL?

easy

A. CREATE TRIGGER trigger_name WHEN INSERT ON table_name EXECUTE function_name();

B. CREATE TRIGGER trigger_name BEFORE UPDATE table_name CALL function_name();

C. CREATE TRIGGER trigger_name ON table_name AFTER DELETE RUN function_name();

D. CREATE TRIGGER trigger_name AFTER INSERT ON table_name EXECUTE FUNCTION function_name();

Solution

1. Step 1: Recall correct trigger syntax in PostgreSQL (used by Supabase)

   The correct syntax uses CREATE TRIGGER, timing (AFTER/BEFORE), event (INSERT/UPDATE/DELETE), ON table, and EXECUTE FUNCTION.

2. Step 2: Match options to syntax

   CREATE TRIGGER trigger_name AFTER INSERT ON table_name EXECUTE FUNCTION function_name(); matches the correct syntax: CREATE TRIGGER name AFTER INSERT ON table EXECUTE FUNCTION func(); others use wrong keywords like CALL, RUN, or WHEN.

3. Final Answer:

   CREATE TRIGGER trigger_name AFTER INSERT ON table_name EXECUTE FUNCTION function_name(); -> Option D

4. Quick Check:

   CREATE TRIGGER ... EXECUTE FUNCTION ... [OK]

Hint: Use EXECUTE FUNCTION, not CALL or RUN in triggers [OK]

Common Mistakes:

• Using CALL or RUN instead of EXECUTE FUNCTION
• Missing ON keyword before table name
• Using WHEN instead of BEFORE or AFTER

3. Given this trigger function in Supabase SQL:

CREATE FUNCTION log_insert() RETURNS trigger AS $$ BEGIN INSERT INTO logs(table_name, action) VALUES (TG_TABLE_NAME, 'insert'); RETURN NEW; END; $$ LANGUAGE plpgsql;

And this trigger:

CREATE TRIGGER after_insert_log AFTER INSERT ON users EXECUTE FUNCTION log_insert();

What happens when a new row is inserted into the users table?

medium

A. A new row is added to the logs table recording the insert action on users

B. The insert into users is blocked and logs table is updated

C. Nothing happens because the trigger is AFTER INSERT

D. The users table row is deleted after insert

Solution

1. Step 1: Understand the trigger function behavior

   The function inserts a row into logs with the table name and action 'insert' whenever triggered.

2. Step 2: Understand the trigger timing and event

   The trigger runs AFTER INSERT on users, so after a new user row is added, the function runs and logs the action.

3. Final Answer:

   A new row is added to the logs table recording the insert action on users -> Option A

4. Quick Check:

   AFTER INSERT triggers log insert action [OK]

Hint: AFTER INSERT triggers run after data is added [OK]

Common Mistakes:

• Thinking AFTER INSERT blocks the insert
• Assuming trigger does nothing
• Confusing trigger timing with BEFORE

4. You wrote this trigger function:

CREATE FUNCTION update_timestamp() RETURNS trigger AS $$ BEGIN NEW.updated_at = NOW(); RETURN NEW; END; $$ LANGUAGE plpgsql;

And this trigger:

CREATE TRIGGER update_time BEFORE UPDATE ON orders EXECUTE FUNCTION update_timestamp();

But the updated_at column is not changing on updates. What is the likely problem?

medium

A. The trigger is AFTER UPDATE instead of BEFORE UPDATE

B. The trigger function is missing RETURN OLD

C. The trigger function does not modify NEW row correctly

D. The trigger function is not marked as VOLATILE

Solution

1. Step 1: Check how NEW row is modified in trigger

   The function sets NEW.updated_at = NOW() but does not assign it back properly; in PL/pgSQL, you must assign NEW.updated_at and then RETURN NEW.

2. Step 2: Confirm trigger timing and return

   The trigger is BEFORE UPDATE and returns NEW, which is correct. The problem is likely the function does not properly update the NEW record.

3. Final Answer:

   The trigger function does not modify NEW row correctly -> Option C

4. Quick Check:

   Modify NEW row correctly in BEFORE UPDATE triggers [OK]

Hint: Always RETURN NEW after modifying it in BEFORE UPDATE triggers [OK]

Common Mistakes:

• Not returning NEW after changes
• Using AFTER UPDATE instead of BEFORE UPDATE
• Returning OLD instead of NEW

5. You want to automatically archive deleted rows from the products table into products_archive using a trigger. Which approach correctly achieves this in Supabase?

hard

A. Create an AFTER DELETE trigger on products that inserts OLD row into products_archive

B. Create a BEFORE DELETE trigger on products that deletes from products_archive

C. Create an AFTER INSERT trigger on products_archive that copies rows to products

D. Create a BEFORE UPDATE trigger on products that moves rows to products_archive

Solution

1. Step 1: Understand the goal

   You want to save deleted rows from products into products_archive automatically.

2. Step 2: Choose correct trigger timing and action

   AFTER DELETE trigger on products can access OLD row data and insert it into products_archive. BEFORE DELETE is too early to archive after deletion. Other options do not archive deleted rows.

3. Final Answer:

   Create an AFTER DELETE trigger on products that inserts OLD row into products_archive -> Option A

4. Quick Check:

   AFTER DELETE triggers archive OLD row [OK]

Hint: Use AFTER DELETE triggers to archive deleted rows [OK]

Common Mistakes:

• Using BEFORE DELETE to archive after deletion
• Confusing insert and delete triggers
• Trying to archive on update instead of delete