« W3Schools Home Next Chapter » SQL SQL is a standard language for accessing databases. Our SQL tutorial will teach you how to use SQL to access and manipulate data in: MySQL, SQL Server, Access, Oracle, Sybase, DB2, and other database systems....
At W3Schools you will find a complete reference for keywords and functions: SQL Keyword Reference MYSQL Functions SQLServer Functions MS Access Functions SQL Quick Reference SQL Data Types Data types and ranges for Microsoft Access, MySQL and SQL Server. ...
SQL Server:微软的关系型数据库,广泛应用于企业级应用。 Oracle:大规模应用的高性能数据库,适合处理复杂事务和大数据。 二、SQL 语言简介:查询、插入、更新、删除(CRUD 操作) SQL(Structured Query Language)是用于操作关系型数据库的标准语言。通过SQL,我们可以进行数据查询(SELECT)、数据插入(INSERT)、数据更新(UPDAT...
SQL Statement: SELECT * FROM Customers ORDER BY CustomerName ASC; Edit the SQL Statement, and click "Run SQL" to see the result. Run SQL » Result: Click "Run SQL" to execute the SQL statement above. W3Schools has created an SQL database in your browser. The menu to the rig...
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Any operation performed with NULL results in NULL. Different databases have different functions to handle null. There is a common function that is used in MySQL, Microsoft SQL Server, and Oracle to treat NULLs. SELECT ename, sal+COALESCE(comm,0) FROM employee; Output: ENAME SAL+COALESCE(COMM...
Obviously if the stored procedure language is C#, Java, or R, you’re going to use the functions and syntax of those procedural languages. In other words, despite the fact that the motivation for SQL was to use standardized declarative queries, in the real world you see lots of database-...
SQL Tutorial——w3schools (示例教程)入门之后,就要多学学T-SQL语言了。除了51自学网的SQL Server数据库教程外,w3schools是一个很好的资源库,它不止讲解T-SQL语言的知识点,还有一个在线的示例数据库提供给用户,可以随时随地进行练习。 Head First SQL——Head First系列(文字教程)因为是文字教程,所以贴的是豆瓣...
[Advanced] SQL Window Functions [Advanced] SQL Advanced JOINS & Performance Tuning 下面以第一节课为例,老师先是通过视频的形式讲解相关的概念: 美国人嘛,自然语音纯正,听起来也容易,毕竟SQL的内容也不是很难。 再附上清晰的必要文字讲解: 再提供一些知识测试: 加上文字材料: 然后就是必要的query statements...
统计函数 aggregate functions 不能用WHERE语句,可以用于HAVING语句 MAX()SUM()MIN()AVG() 算术 /除法,注意小数位数与除数、被除数中最长的数据类型一致,例如:4/3=1,4.0/3.0=1.333...,4/3.0=1.333...。 ROUND(number, digits) 保留某数字(number)小数点后digits位数 ...