Shulou(Shulou.com)06/01 Report--

About 1.SQL SQL is the acronym of Structured Query Language (structured query language). SQL is a database language. Oracle uses this language to store and retrieve information. Through SQL, the communication table with the Oracle server is the main database object for storing data.

SQL supports the following categories of commands

Data definition language (DDL): CREATE ALTER DROP

Data manipulation language (DML): INSERT DELETE UPDATE SELECT

Transaction Control language (TCL): COMMIT ROLLBACK

Data Control language (DCL): GRANT REVOKE

two。 Data definition language

The data definition language is used to change the database structure, including creating, changing, and deleting database objects

The data definition language commands for manipulating table structures are:

CREATE TABLE create table

ALTER TABLE modify table

It is efficient for TRUNCATE TABLE to delete the data log from the table only once.

DROP TABLE delete table

2.1 create table create table emp (emp_id NUMBER (10) not null,-- employee number emp_name VARCHAR2 (100),-- employee name emp_sex VARCHAR2 (5),-- employee gender emp_birthday DATE,-- birthday emp_salary DATE,-- salary primary key (emp_id)-- Primary key) 2.2 modify table alter table table name add constraint field primary key (field) -- set primary key alter table USER_INFO modify USER_NAME VARCHAR2 (500);-- modify field length 2.3Delete table records

TRUNCATE TABLE table name

TRUNCATE TABLE USER_INFO

2.4 Delete the table

DROP TABLE table name

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