Soft delete pattern concept in SQL - Step-by-Step Execution

Concept Flow - Soft delete pattern concept

Start: User wants to delete a record

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Update record's 'deleted' flag to TRUE

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Record remains in table but marked deleted

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Queries filter out records where 'deleted' is TRUE

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Deleted records hidden from normal views

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Optionally, restore by setting 'deleted' to FALSE

Soft delete means marking a record as deleted instead of removing it, so it stays in the table but is hidden from normal queries.

Execution Sample

SQL

UPDATE users
SET deleted = TRUE
WHERE id = 3;

SELECT * FROM users
WHERE deleted = FALSE;

Marks user with id=3 as deleted, then selects only users not marked deleted.

Execution Table

Step	Action	SQL Executed	Table State	Output
1	Mark user id=3 as deleted	UPDATE users SET deleted = TRUE WHERE id = 3;	User 3: deleted=TRUE; others deleted=FALSE	No output (update)
2	Select users not deleted	SELECT * FROM users WHERE deleted = FALSE;	Same as above	Returns all users except user 3
3	Attempt to select all users without filter	SELECT * FROM users;	Same as above	Returns all users including deleted ones
4	Restore user id=3	UPDATE users SET deleted = FALSE WHERE id = 3;	User 3: deleted=FALSE; others deleted=FALSE	No output (update)
5	Select users not deleted after restore	SELECT * FROM users WHERE deleted = FALSE;	Same as above	Returns all users including user 3

💡 Execution stops after restoring user and selecting active users.

Variable Tracker

Variable	Start	After Step 1	After Step 4	Final
deleted flag for user 3	FALSE	TRUE	FALSE	FALSE

Key Moments - 3 Insights

Why doesn't the DELETE statement remove the record?

Because soft delete uses UPDATE to set a 'deleted' flag instead of DELETE, so the record stays in the table but is marked as deleted (see execution_table step 1).

How do queries exclude deleted records?

By adding WHERE deleted = FALSE in SELECT queries, only records not marked deleted are returned (see execution_table step 2).

Can a deleted record be restored?

Yes, by updating the 'deleted' flag back to FALSE, the record becomes active again (see execution_table step 4).

Visual Quiz - 3 Questions

Look at the execution_table, what is the 'deleted' flag value for user 3 after step 1?

A TRUE

B FALSE

C NULL

D UNKNOWN

💡 Hint

Check the 'Table State' column in execution_table row for step 1.

At which step does the SELECT query return all users including the deleted one?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Look at the 'Output' column in execution_table rows for steps 2 and 3.

If we forget to add WHERE deleted = FALSE in SELECT, what happens?

A Query returns no records

B Deleted records are included in results

C Query fails with error

D Only deleted records are returned

💡 Hint

See execution_table step 3 where SELECT without filter returns all records.

Concept Snapshot

Soft delete means marking a record as deleted using a flag (e.g., deleted=TRUE) instead of removing it.
Use UPDATE to set the flag.
SELECT queries filter out deleted records with WHERE deleted=FALSE.
Deleted records remain in the table and can be restored by resetting the flag.
This preserves data and allows easy recovery.

Full Transcript

Soft delete pattern means when you want to delete a record, you don't remove it from the database. Instead, you mark it as deleted by setting a special flag, like a 'deleted' column to TRUE. This way, the record stays in the table but is hidden from normal queries. When you select data, you add a condition to only get records where deleted is FALSE. If you want to restore a deleted record, you just set the flag back to FALSE. This pattern helps keep data safe and recoverable. The example shows updating user id 3 to deleted=TRUE, then selecting only users not deleted, so user 3 is hidden. Later, user 3 is restored by setting deleted=FALSE again.