SQL, Java, Polymorphism, Joins | Dataford Interview Questions

SQL, Java, polymorphism, Joins.

Use the schema below to treat account_type as a discriminator for polymorphic account behavior. Write a PostgreSQL query that returns every open account, including accounts without qualifying events. Include only events posted during 2025; account-level totals must remain zero when no such events exist.

Output

One row per open account with customer_name, account_id, account_type, account_label, event_count, and total_amount
account_label must identify the account type, and NULL event amounts must not inflate totals
Sort by customer_name, then account_id ascending

Schema

customers

Column	Type	Description
customer_idPK	INT	Unique customer identifier
customer_name	VARCHAR(100)	Customer's full name

accounts

Column	Type	Description
account_idPK	INT	Unique account identifier
customer_id	INT	Owning customer identifier
account_type	VARCHAR(30)	Polymorphic account discriminator
status	VARCHAR(20)	Current account status

account_events

Column	Type	Description
event_idPK	INT	Unique account event identifier
account_id	INT	Related account identifier
event_type	VARCHAR(30)	Type of account activity
posted_at	DATE	Date the event was posted
amount	NUMERIC(12,2)	Event amount, which may be NULL

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