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TOP子句用于规定要返回的记录的数目。 SELECT TOP number | percent column_name FROM table_name LIKE操作符用于在WHERE子句中搜索列的指定模式。 SELECT column_name FROM table_name WHERE colum 阅读全文
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Question: Suppose that a website contains two tables, the Customers table and the Orders table. Write a SQL query to find all customers who never orde 阅读全文
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SQL JOIN:用于根据两个或多个表中列的关系,从这些表中查数据。 (为了得到完整数据,我们需要从两个或多个表中获取结果。) 例如W3School中列出的实例,使用如下语句: select Persons.LastName, Persons.FirstName, Orders.OrderNo fr 阅读全文
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Question: Write a SQL query to get the second highest salary from the Employee table. +----+--------+ | Id | Salary | +----+--------+ | 1 | 100 | | 2 阅读全文
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Question: The Employee table holds all employees including their managers. Every employee has an Id, and there is also a column for the manager Id. +- 阅读全文
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SQL Count()函数: SQL COUNT(column_name)语法:COUNT(column_name)函数返回指定列的值得数目(NULL不计入) select count(column_name) from table_name SQL COUNT(DISTINCT column_na 阅读全文
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SQL INNER JOIN 关键字 在表中存在至少一个匹配时,INNER JOIN关键字返回行。 INNER JIN关键字语法 SELECT column_name(s) FROM table_name1 INNER JOIN table_name2 ON table_name1.column_n 阅读全文
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Question: Given a Weather table, write a SQL query to find all dates' Ids with higher temperature compared to its previous (yesterday's) dates. +----- 阅读全文
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SQL对大小写不敏感! SQL DML和DDL:可以把SQL分为两个部分:数据操作语言(DML)和数据定义语言(DDL) SQL(结构化查询语言)是用于执行查询的语法。但是SQL语言也包含用于更新、插入和删除记录的语法。 查询和更新指令构成了SQL的DML部分: select,update,dele 阅读全文