以下是对Oracle中的创建和管理表进行了详细的分析介绍，需要的朋友可以过来参考下 SQL /* SQL 对于表的操作: 创建表，修改表(添加新的列，改变当前某些列，删除列),删除表 SQL 创建表: create table(需要create table的权限) SQL 修改表: alter table tabl
以下是对Oracle中的创建和管理表进行了详细的分析介绍，需要的朋友可以过来参考下
SQL> /*
SQL> 对于表的操作: 创建表，修改表(添加新的列，改变当前某些列，删除列),删除表
SQL> 创建表: create table(需要create table的权限)
SQL> 修改表: alter table tablename add/modify/drop
SQL> 删除表：drop table tablename
SQL> */
SQL> show user;
USER 为 "SCOTT"
SQL> --访问hr用户下的表
SQL> select * from hr.employees;
select * from hr.employees
*
第 1 行出现错误:
ORA-00942: 表或视图不存在
SQL> --测试defaul值
SQL> create table test1
2 (tid number,
3 tname varchar(20),
4 hiredate date default sysdate);
表已创建。
SQL> insert into test1(tid,tname) values(1,'Mary');
已创建 1 行。
SQL> select * from test1;
TID TNAME HIREDATE
---------- -------------------- --------------
1 Mary 12-6月 -11
SQL> --rowid rownum都是伪列
SQL> select rowid,rownum,empno from emp;
ROWID ROWNUM EMPNO
------------------ ---------- ----------
AAANA2AAEAAAAAsAAT 1 1122
AAANA2AAEAAAAAsAAO 2 1234
AAANA2AAEAAAAAsAAP 3 1235
AAANA2AAEAAAAAsAAQ 4 2222
AAANA2AAEAAAAAsAAR 5 2345
AAANA2AAEAAAAAsAAS 6 2346
AAANA2AAEAAAAAsAAA 7 7369
AAANA2AAEAAAAAsAAB 8 7499
AAANA2AAEAAAAAsAAC 9 7521
AAANA2AAEAAAAAsAAD 10 7566
AAANA2AAEAAAAAsAAE 11 7654
ROWID ROWNUM EMPNO
------------------ ---------- ----------
AAANA2AAEAAAAAsAAF 12 7698
AAANA2AAEAAAAAsAAG 13 7782
AAANA2AAEAAAAAsAAH 14 7788
AAANA2AAEAAAAAsAAI 15 7839
AAANA2AAEAAAAAsAAJ 16 7844
AAANA2AAEAAAAAsAAK 17 7876
AAANA2AAEAAAAAsAAL 18 7900
AAANA2AAEAAAAAsAAM 19 7902
AAANA2AAEAAAAAsAAN 20 7934
已选择20行。
SQL> --rowid:oracle维护一个地址，该地址指向了该行在硬盘上实际存储的位置
SQL> --关于varchar2和char
SQL> create table testchar
2 ( c char(5),
3 v varchar(5));
表已创建。
SQL> insert into testchar values('a','b');
已创建 1 行。
SQL> select * from testchar;
C V
----- -----
a b
SQL> select concat(c,'#'),concat(v,'#') from testchar;
CONCAT CONCAT
------ ------
a # b#
SQL> --添加新列
SQL> alter table testchar
2 add hiredate date;
表已更改。
SQL> desc testchar;
名称 是否为空? 类型
----------------------------------------------------------------- -------- --------------------------------------------
C CHAR(5)
V VARCHAR2(5)
HIREDATE DATE
SQL> --修改表
SQL> alter table testchar
2 modify c char(10);
表已更改。
SQL> desc testchar;
名称 是否为空? 类型
----------------------------------------------------------------- -------- --------------------------------------------
C CHAR(10)
V VARCHAR2(5)
HIREDATE DATE
SQL> --删除列
SQL> alter table testchar
2 drop hiredate;
drop hiredate
*
第 2 行出现错误:
ORA-00905: 缺失关键字
SQL> ed
已写入 file afiedt.buf
1 alter table testchar
2* drop column hiredate
SQL> /
表已更改。
SQL> desc testchar;
名称 是否为空? 类型
----------------------------------------------------------------- -------- --------------------------------------------
C CHAR(10)
V VARCHAR2(5)
SQL> host cls
SQL> --删除表
SQL> select * from tab;
TNAME TABTYPE CLUSTERID
------------------------------ ------- ----------
DEPT TABLE
EMP TABLE
BONUS TABLE
SALGRADE TABLE
EMP10 TABLE
EMP101 TABLE
TEST1 TABLE
BIN$gNM24ey8RKW0vjhtZ7ZFsA==$0 TABLE
TESTDELETE TABLE
TESTCHAR TABLE
已选择10行。
SQL> drop table testdelete;
表已删除。
SQL> select * from tab;
TNAME TABTYPE CLUSTERID
------------------------------ ------- ----------
DEPT TABLE
EMP TABLE
BONUS TABLE
SALGRADE TABLE
EMP10 TABLE
EMP101 TABLE
TEST1 TABLE
BIN$gNM24ey8RKW0vjhtZ7ZFsA==$0 TABLE
TESTCHAR TABLE
BIN$aJrS9iffT4O1GcD0H3fepg==$0 TABLE
已选择10行。
SQL> --使用purge参数彻底删除表
SQL> drop table test1 purge;
表已删除。
SQL> select * from tab;
TNAME TABTYPE CLUSTERID
------------------------------ ------- ----------
DEPT TABLE
EMP TABLE
BONUS TABLE
SALGRADE TABLE
EMP10 TABLE
EMP101 TABLE
BIN$gNM24ey8RKW0vjhtZ7ZFsA==$0 TABLE
TESTCHAR TABLE
BIN$aJrS9iffT4O1GcD0H3fepg==$0 TABLE
已选择9行。
SQL> --oracle的回收站
SQL> --查看回收站
SQL> show recyclebin;
ORIGINAL NAME RECYCLEBIN NAME OBJECT TYPE DROP TIME
---------------- ------------------------------ ------------ -------------------
TESTDELETE BIN$aJrS9iffT4O1GcD0H3fepg==$0 TABLE 2011-06-12:15:43:34
TESTDELETE BIN$gNM24ey8RKW0vjhtZ7ZFsA==$0 TABLE 2011-06-12:14:51:43
SQL> --清空回收站
SQL> purge recyclebin;
回收站已清空。
SQL> show recyclebin;
SQL> --关于约束:
SQL> --创建一个表，包含所有约束
SQL> create table myuser
2 ( userID number constraint pk primary key,
3 username varchar2(20) constraint c_name not null,
4 gender varchar2(2) constraint c_gender check (gender in ('男','女')),
5 email varchar2(20) constraint c_email1 not null
6 constraint c_email2 unique
7 deptno number constraint fk refereneces dept(deptno)
8 );
deptno number constraint fk refereneces dept(deptno)
*
第 7 行出现错误:
ORA-00907: 缺失右括号
SQL> create table myuser
2 ( userID number constraint pk primary key,
3 username varchar2(20) constraint c_name not null,
4 gender varchar2(2) constraint c_gender check (gender in ('男','女')),
5 email varchar2(20) constraint c_email1 not null
6 constraint c_email2 unique,
7 deptno number constraint fk refereneces dept(deptno)
8 );
deptno number constraint fk refereneces dept(deptno)
*
第 7 行出现错误:
ORA-02253: 此处不允许约束条件说明
SQL> ed
已写入 file afiedt.buf
1 create table myuser
2 ( userID number constraint pk primary key,
3 username varchar2(20) constraint c_name not null,
4 gender varchar2(2) constraint c_gender check (gender in ('男','女')),
5 email varchar2(20) constraint c_email1 not null
6 constraint c_email2 unique,
7 deptno number constraint fk references dept(deptno)
8* )
SQL> /
表已创建。
SQL> desc myuser;
名称 是否为空? 类型
----------------------------------------------------------------- -------- --------------------------------------------
USERID NOT NULL NUMBER
USERNAME NOT NULL VARCHAR2(20)
GENDER VARCHAR2(2)
EMAIL NOT NULL VARCHAR2(20)
DEPTNO NUMBER
SQL> insert into myuser values(1,'Tom','男','ddd@126.com',10);
已创建 1 行。
SQL> insert into myuser values(1,'Tom','男','ddd@126.com',10);
insert into myuser values(1,'Tom','男','ddd@126.com',10)
*
第 1 行出现错误:
ORA-00001: 违反唯一约束条件 (SCOTT.PK)
SQL> insert into myuser values(2,'Tom','啊','ddd@126.coddm',10);
insert into myuser values(2,'Tom','啊','ddd@126.coddm',10)
*
第 1 行出现错误:
ORA-02290: 违反检查约束条件 (SCOTT.C_GENDER)
SQL> --触发器也可以检查数据的正确与否
SQL> spool off
How does MySQL index cardinality affect query performance?Apr 14, 2025 am 12:18 AMMySQL index cardinality has a significant impact on query performance: 1. High cardinality index can more effectively narrow the data range and improve query efficiency; 2. Low cardinality index may lead to full table scanning and reduce query performance; 3. In joint index, high cardinality sequences should be placed in front to optimize query.
MySQL: Resources and Tutorials for New UsersApr 14, 2025 am 12:16 AMThe MySQL learning path includes basic knowledge, core concepts, usage examples, and optimization techniques. 1) Understand basic concepts such as tables, rows, columns, and SQL queries. 2) Learn the definition, working principles and advantages of MySQL. 3) Master basic CRUD operations and advanced usage, such as indexes and stored procedures. 4) Familiar with common error debugging and performance optimization suggestions, such as rational use of indexes and optimization queries. Through these steps, you will have a full grasp of the use and optimization of MySQL.
Real-World MySQL: Examples and Use CasesApr 14, 2025 am 12:15 AMMySQL's real-world applications include basic database design and complex query optimization. 1) Basic usage: used to store and manage user data, such as inserting, querying, updating and deleting user information. 2) Advanced usage: Handle complex business logic, such as order and inventory management of e-commerce platforms. 3) Performance optimization: Improve performance by rationally using indexes, partition tables and query caches.
SQL Commands in MySQL: Practical ExamplesApr 14, 2025 am 12:09 AMSQL commands in MySQL can be divided into categories such as DDL, DML, DQL, DCL, etc., and are used to create, modify, delete databases and tables, insert, update, delete data, and perform complex query operations. 1. Basic usage includes CREATETABLE creation table, INSERTINTO insert data, and SELECT query data. 2. Advanced usage involves JOIN for table joins, subqueries and GROUPBY for data aggregation. 3. Common errors such as syntax errors, data type mismatch and permission problems can be debugged through syntax checking, data type conversion and permission management. 4. Performance optimization suggestions include using indexes, avoiding full table scanning, optimizing JOIN operations and using transactions to ensure data consistency.
How does InnoDB handle ACID compliance?Apr 14, 2025 am 12:03 AMInnoDB achieves atomicity through undolog, consistency and isolation through locking mechanism and MVCC, and persistence through redolog. 1) Atomicity: Use undolog to record the original data to ensure that the transaction can be rolled back. 2) Consistency: Ensure the data consistency through row-level locking and MVCC. 3) Isolation: Supports multiple isolation levels, and REPEATABLEREAD is used by default. 4) Persistence: Use redolog to record modifications to ensure that data is saved for a long time.
MySQL's Place: Databases and ProgrammingApr 13, 2025 am 12:18 AMMySQL's position in databases and programming is very important. It is an open source relational database management system that is widely used in various application scenarios. 1) MySQL provides efficient data storage, organization and retrieval functions, supporting Web, mobile and enterprise-level systems. 2) It uses a client-server architecture, supports multiple storage engines and index optimization. 3) Basic usages include creating tables and inserting data, and advanced usages involve multi-table JOINs and complex queries. 4) Frequently asked questions such as SQL syntax errors and performance issues can be debugged through the EXPLAIN command and slow query log. 5) Performance optimization methods include rational use of indexes, optimized query and use of caches. Best practices include using transactions and PreparedStatemen
MySQL: From Small Businesses to Large EnterprisesApr 13, 2025 am 12:17 AMMySQL is suitable for small and large enterprises. 1) Small businesses can use MySQL for basic data management, such as storing customer information. 2) Large enterprises can use MySQL to process massive data and complex business logic to optimize query performance and transaction processing.
What are phantom reads and how does InnoDB prevent them (Next-Key Locking)?Apr 13, 2025 am 12:16 AMInnoDB effectively prevents phantom reading through Next-KeyLocking mechanism. 1) Next-KeyLocking combines row lock and gap lock to lock records and their gaps to prevent new records from being inserted. 2) In practical applications, by optimizing query and adjusting isolation levels, lock competition can be reduced and concurrency performance can be improved.
Hot AI Tools
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Undress AI Tool
Undress images for free
Clothoff.io
AI clothes remover
AI Hentai Generator
Generate AI Hentai for free.
Hot Article
Hot Tools
MantisBT
Mantis is an easy-to-deploy web-based defect tracking tool designed to aid in product defect tracking. It requires PHP, MySQL and a web server. Check out our demo and hosting services.
Atom editor mac version download
The most popular open source editor
SublimeText3 Linux new version
SublimeText3 Linux latest version
DVWA
Damn Vulnerable Web App (DVWA) is a PHP/MySQL web application that is very vulnerable. Its main goals are to be an aid for security professionals to test their skills and tools in a legal environment, to help web developers better understand the process of securing web applications, and to help teachers/students teach/learn in a classroom environment Web application security. The goal of DVWA is to practice some of the most common web vulnerabilities through a simple and straightforward interface, with varying degrees of difficulty. Please note that this software
mPDF
mPDF is a PHP library that can generate PDF files from UTF-8 encoded HTML. The original author, Ian Back, wrote mPDF to output PDF files "on the fly" from his website and handle different languages. It is slower than original scripts like HTML2FPDF and produces larger files when using Unicode fonts, but supports CSS styles etc. and has a lot of enhancements. Supports almost all languages, including RTL (Arabic and Hebrew) and CJK (Chinese, Japanese and Korean). Supports nested block-level elements (such as P, DIV),
