Oracle Course archive, day fifth

Collection operations

Desc job_history: Changing the position of history

Job_history: History table

Vnion: Duplicate values retain only one remove duplicate value ★

Vnion all: Retain all duplicate values without removing duplicate values ★

Intersect: Intersect

Minus: minus

Double quotation marks to the nonstandard object name ★

Single quotation mark is a string ★

DESC departments Query what columns are in the Department table

Desc employees query What columns are in the employee table

Select employee_id, job_id from Employees
UNION ALL
Select employee_id, job_id from Job_history;

Select employee_id, job_id from Employees
Union
Select employee_id, job_id from Job_history;

Select employee_id, job_id from Employees
Intersect
Select employee_id, job_id from Job_history;

Select employee_id from Employees
Minus
Select employee_id from Job_history;

Select employee_id, job_id, salary from employees
UNION ALL
Select employee_id, job_id, null from job_history;

Select employee_id, job_id, To_char (salary) from employees
UNION ALL
Select employee_id, job_id, ' no salary ' from job_history;

Collection Sort:
Select employee_id, job_id, salary from employees
UNION ALL
Select employee_id, job_id, null from Job_history
Order by salary;

Select employee_id, job_id, null from Job_history
UNION ALL
Select employee_id, job_id, salary from employees
Order by 3;

Salary null and Sky value personal understanding

To create a table:

CREATE TABLE: Creating tables

INSERT INTO: inserting

Update: Updates

Delete: Remove data from table

Drop: Delete Table

Constraint: Constraint commit: Commit the creation of the table after the completion of the commit must be committed;

NOT null: Non-empty

View: Views drop sequence course_cid; Delete the name of the increment if you repeat, use this to delete the duplicate name Coure_cid created for you to delete.

Sequence: Sequence

Uniquenes: Uniqueness of start with: from .... Begin

VARCHAR2: Long characters

Modify: Modify, add

Primary key (primary key) constraints, foreign key (foreign key) constraints, unique (unique) constraints, check constraints, defaults (default) constraint instances

There are several types of constraints:
C (check constraint on a table)
P (primary key)
U (Unique key)
R (referential AKA Foreign Key)
V (with CHECK option, on a view)
O (with Read only, on a view)

Dml

X: first column + data type

Y: Second column + character type--character type must be enclosed in single quotation marks

Z: Third column + Date type

SELECT * from + table name + What to look for

desc+ table name can also be checked

Delete table: drop table + tables name

User_table: Name of all tables under current user

Delete Row (delete data): Delete from table + which row

Ddl

Modify Table Structure

ALTER TABLE T1 xxxxxx★★

Delete column: Alter t1 drop X

CREATE TABLE T1 (x (column name) int (type) constraint (constraint) T1_X_PK (the name of the constraint) PrimaryKey (primary key));

Oracle Course archive, day fifth