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Problem
Table: Accounts
+---------------+---------+
| Column Name | Type |
+---------------+---------+
| account_id | int |
| account_name | varchar |
+---------------+---------+
account_id is the primary key (column with unique values) for this table.
Each row of this table contains the ID and the name of an account in the bank.
Table: Transactions
+---------------+---------+
| Column Name | Type |
+---------------+---------+
| transaction_id| int |
| account_id | int |
| transaction_date | date |
+---------------+---------+
transaction_id is the primary key (column with unique values) for this table.
Each row of this table contains the ID of a transaction, the ID of the account that initiated the transaction, and the date when the transaction was made.
Problem Definition
Write a solution to find all accounts that did not make any transactions in 2020
.
Return the result table ordered by account_name
in ascending order.
Example
Input:
Accounts table:
+------------+--------------+
| account_id | account_name |
+------------+--------------+
| 1 | Alice |
| 2 | Bob |
| 3 | Charlie |
+------------+--------------+
Transactions table:
+----------------+------------+-----------------+
| transaction_id | account_id | transaction_date|
+----------------+------------+-----------------+
| 1 | 1 | 2020-09-01 |
| 2 | 2 | 2020-09-02 |
| 3 | 1 | 2020-09-03 |
| 4 | 3 | 2019-08-21 |
| 5 | 2 | 2021-07-03 |
+----------------+------------+-----------------+
Output:
+--------------+
| account_name |
+--------------+
| Charlie |
+--------------+
Try It Yourself
Solution
To identify all accounts that did not make any transactions in the year 2020, we can leverage SQL's LEFT JOIN
along with conditional filtering. This approach allows us to include all accounts and exclude those that have associated transactions in the specified year.
- Perform a Left Join Between Accounts and Transactions: Join the
Accounts
table with theTransactions
table onaccount_id
, focusing only on transactions that occurred in 2020. - Filter Accounts Without Transactions in 2020: Identify accounts that have no matching transactions in the year 2020 by checking for
NULL
values in the joinedTransactions
data. - Order the Results by Account Name: Sort the final list of accounts alphabetically by
account_name
for organized presentation.
SQL Query
SELECT A.account_name FROM Accounts AS A LEFT JOIN Transactions AS T ON A.account_id = T.account_id AND YEAR(transaction_date) = '2020' WHERE T.account_id IS NULL ORDER BY account_name ASC;
Step-by-Step Approach
Step 1: Perform a Left Join Between Accounts and Transactions for the Year 2020
Combine the Accounts
and Transactions
tables to associate each account with its transactions in the year 2020. The LEFT JOIN
ensures that all accounts are included, even if they have no transactions in 2020.
SQL Query:
SELECT A.account_name, T.account_id FROM Accounts AS A LEFT JOIN Transactions AS T ON A.account_id = T.account_id AND YEAR(transaction_date) = '2020';
Explanation:
SELECT A.account_name, T.account_id
:-
Retrieves the
account_name
from theAccounts
table and the correspondingaccount_id
from theTransactions
table.
-
LEFT JOIN Transactions AS T
:- Performs a
LEFT JOIN
with theTransactions
table, aliased asT
, ensuring all accounts are included regardless of transaction activity.
- Performs a
ON A.account_id = T.account_id AND YEAR(transaction_date) = '2020'
:- Defines the join condition to match accounts with their transactions in the year 2020.
Output After Step 1:
Assuming the example input provided, the intermediate result after the LEFT JOIN
would be:
+--------------+------------+ | account_name | account_id | +--------------+------------+ | Alice | 1 | | Bob | 2 | | Charlie | NULL | +--------------+------------+
Step 2: Filter Accounts Without Transactions in 2020
Identify accounts that did not make any transactions in 2020 by selecting records where the joined Transactions
data is NULL
.
SQL Query:
SELECT A.account_name FROM Accounts AS A LEFT JOIN Transactions AS T ON A.account_id = T.account_id AND YEAR(transaction_date) = '2020' WHERE T.account_id IS NULL;
Explanation:
WHERE T.account_id IS NULL
:- Filters the results to include only those accounts that have no corresponding transactions in 2020. If
T.account_id
isNULL
, it indicates no transaction record exists for that account in the specified year.
- Filters the results to include only those accounts that have no corresponding transactions in 2020. If
Output After Step 2:
Based on the intermediate result, the filtered output would be:
+--------------+ | account_name | +--------------+ | Charlie | +--------------+
Step 3: Order the Results by Account Name in Ascending Order
Sort the final list of accounts alphabetically by account_name
to present the data in an organized and readable manner.
SQL Query:
ORDER BY account_name ASC;
Explanation:
ORDER BY account_name ASC
:- Sorts the resulting list of account names in ascending (alphabetical) order.
Final Output:
+--------------+ | account_name | +--------------+ | Charlie | +--------------+
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