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    Top 10 Databases You Should Learn in 2020

    A database is must need for any software development and which database to choose is one of the main requirement for software architecture. In...

    Customers Who Never Order

    Suppose that a website contains two tables, the tableCustomers and the tableOrders. Write a SQL query to find all customers who never order anything. Table:...

    Employees Earning More Than Their Managers

    The Employee table holds all employees including their managers. Every employee has an Id, and there is also a column for the manager Id. +----+-------+--------+-----------+ |...

    Delete Duplicate Emails

    Write a SQL query to delete all duplicate email entries in a table named,Person keeping only unique emails based on its smallestId. +----+------------------+ | Id | Email...

    Rising Temperature

    Given a Weather table, write a SQL query to find all dates' Ids with higher temperature compared to its previous (yesterday's) dates. +---------+------------+------------------+ | Id(INT) | Date(DATE) |...

    Department Highest Salary

    The Employee table holds all employees. Every employee has an Id, a salary, and there is also a column for the department Id. +----+-------+--------+--------------+ | Id | Name...

    Swap Sex Field

    Given a table salary, such as the one below, that has m=male and f=female values. Swap all f and m values (i.e., change all f...

    Combine Two Tables

    Table: Person +-------------+---------+ | Column Name | Type | +-------------+---------+ | PersonId | int | | FirstName |...

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