SQL 是 Structure Query Language(结构化查询语言)的缩写,它是关系模型数据库的一门应用语言。经长期发展,SQL语言标准日趋完善,SQL已然成为一种十分受欢迎的多平台交互底层会话语言。 SQL语句主要可以划分为以下三个类别: DDL(Data Definition Language)数据定义语言:用于定义不同的数据段、数据库、表、视图、索引等数...
上面的 DDL 有几个地方需要强调一下: 首先,上面 SQL 中的数据库名、表名、字段名都被反引号(`)包裹起来,反引号并不是必须的,但是却可以解决表名、字段名等跟 SQL 关键字冲突的问题。 创建数据库时,我们通过default character set utf8mb4指定了数据库默认使用的字符集为utf8mb4(最大4字节的utf-8编码),...
1、背景 最近公司为了降本,在做presto sql到spark sql的任务迁移(体力活 ),作为一个两年多来一直在用presto的sql boy,因为presto本身是针对adhoc场景,所以在平时建表的时候都是简单粗暴的create table table_name as 、 insert into table_name 等等, 最近上线了spark之后,发现了spark在etl的强大,也发现其实自己...
DML, DDL, TCL and DQL and it’s subtypes. We’ve gone through each command in detail with its syntax and example that will assist you in writing queries. The SQL commands’ allows you to construct and manipulate a wide range of database objects with the different commands. After going th...
*Example:*TransactionId t commits and has subxids t1,t2,t3,t4*t is on page p1,t1 is also on p1,t2 and t3 are on p2,t4 is on p3*1.update pages2-3:*page2:sett2,t3assub-committed*page3:sett4assub-committed*2.update page1:*sett1assub-committed,*thensettascommitted,thensett1as...
CREATE Command in SQL SQL Create the database or its object (ie table, index, view, function, etc.). Syntax CREATE DATABASE databasename Example CREATE DATABASE Student_data; SQL Copy Syntax CREATE TABLE table_name ( column1 datatype, column2 datatype, column3 datatype, ... ); Examp...
Here, the SQL command adds a column namedemailto theCustomerstable. iii. DROP TABLE In SQL, theDROP TABLEcommand is used to delete the specified table in our database. For example, -- delete Orders tableDROPTABLEOrders; Run Code Here, the SQL command will delete the table namedOrders. ...
例(选用example数据库) 2)查看已选择的数据库中所有数据表 基本语法:SHOW TABLES; 例(查看test1数据库中数据表) 3)删除数据库 基本语法:DROP DATABASE dbname; 例(删除test1数据库) (二)数据表操作 1.创建表 基本语法: CREATE TABLE tablename(
You can control how Import runs by entering the'impdp'command followedby various parameters.To specify parameters,you use keywords:Format:impdpKEYWORD=value orKEYWORD=(value1,value2,...,valueN)Example:impdp scott/tigerDIRECTORY=dmpdirDUMPFILE=scott.dmpUSERIDmust be the first parameter on the comm...
DDL statements in SQL primarily consist of the CREATE, ALTER, and DROP commands. Let's take a closer look at each of these commands and their usage.The CREATE command is used to createnew database objects such as tables, views, indexes, and stored procedures. For example, to create a ...