Nightonke's Blog

Write a SQL query to find all duplicate emails in a table named Person.+----+---------+| Id | Email |+----+---------+| 1 | a@b.com || 2 | c@d.com || 3 | a@b.com |+----+---------+For

Write a SQL query to rank scores. If there is a tie between two scores, both should have the same ranking. Note that after a tie, the next ranking number should be the next consecutive integer value.

如果只是简单地从1开始，递增值为1，可以这样写，serail是一种特殊的类型：往Employee中添加值及其结果：如果想设置更加详细的项，比如起始、递增值、最大值、最小值，可以定义一个sequence。在sequence中，如果是no minvalue、no maxvalue表示最小最大值为-1，注意最小值不能大于最大值.。然后改变表格的列：往E

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

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(DA

Write a SQL query to find all numbers that appear at least three times consecutively.+----+-----+| Id | Num |+----+-----+| 1 | 1 || 2 | 1 || 3 | 1 || 4 | 2 || 5 | 1 || 6 | 2

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

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 | Salary | Departme

Suppose that a website contains two tables, the Customers table and the Orders table. Write a SQL query to find all customers who never order anything.Table: Customers.+----+-------+| Id | Na

Table: Person+-------------+---------+| Column Name | Type |+-------------+---------+| PersonId | int || FirstName | varchar || LastName | varchar |+-------------+---------+Per

Write a SQL query to get the nth highest salary from the Employee table.+----+--------+| Id | Salary |+----+--------+| 1 | 100 || 2 | 200 || 3 | 300 |+----+--------+For exampl

Write a SQL query to get the second highest salary from the Employee table.+----+--------+| Id | Salary |+----+--------+| 1 | 100 || 2 | 200 || 3 | 300 |+----+--------+For exa

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