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Interview Core Track · Easy · 15 min

Replace Employee ID With The Unique Identifier

Table: Employees +---------------+---------+ | Column Name | Type | +---------------+---------+ | id | int | | name | varchar | +---------------+---------+ i...

Interview Core Track
Easy
15 min
joins

Company labels are directional practice context, not official interview guidance.

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Objective

Practice joins through a IshaSQL-tagged business scenario.

Approach

Use this track to improve speed, edge-case handling, and accuracy under timed conditions.

Company context

Company labels are directional practice context, not official interview guidance.

Prereq: query basics
Prereq: filtering

Table: Employees +---------------+---------+ | Column Name | Type | +---------------+---------+ | id | int | | name | varchar | +---------------+---------+ 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 employee in a company. Table: EmployeeUNI +---------------+---------+ | Column Name | Type | +---------------+---------+ | id | int | | unique_id | int | +---------------+---------+ (id, unique_id) is the primary key (combination of columns with unique values) for this table. Each row of this table contains the id and the corresponding unique id of an employee in the company. Write a solution to show the unique ID of each user, If a user does not have a unique ID replace just show null . Return the result table in any order. The result format is in the following example. Example 1: Input: Employees table: +----+----------+ | id | name | +----+----------+ | 1 | Alice | | 7 | Bob | | 11 | Meir | | 90 | Winston | | 3 | Jonathan | +----+----------+ EmployeeUNI table: +----+-----------+ | id | unique_id | +----+-----------+ | 3 | 1 | | 11 | 2 | | 90 | 3 | +----+-----------+ Output: +-----------+----------+ | unique_id | name | +-----------+----------+ | null | Alice | | null | Bob | | 2 | Meir | | 3 | Winston | | 1 | Jonathan | +-----------+----------+ Explanation: Alice and Bob do not have a unique ID, We will show null instead. The unique ID of Meir is 2. The unique ID of Winston is 3. The unique ID of Jonathan is 1.

Employees
id INT PRIMARY KEY
name VARCHAR(255
EmployeeUNI
id INT
unique_id INT
PRIMARY KEY (id
unique_id
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