Oracle subquery, create, and manage tables

Oracle subquery, create, and manage tables
SummarySubquery:

Single Row subquery: returns a single row
Use Single Row comparison Operators
Multi-row subquery: multi-row subquery returns multiple rows
Multiline operators:
IN, ANY, ALL
If the query result of the subquery is null, no rows are returned.

Create and manage tables: Query Data Dictionary:

View a user-defined table:

SELECT table_nameFROM user_tables;

View user-defined data objects:

SELECT distinct object_typeFROM user_objects;

View user-defined tables, views, synonyms, and Sequences

SELECT *FROM user_catalog;

CREATE table
Two methods:

Create table [schema.] table
(Column datatype [DEFAULT expr] [,…]); Create table table
[(Column, column…)]
AS subquery;

ALTER table

Alter table table
ADD (column datatype [DEFAULT expr]
[, Column datatype]…); Alter table table
MODIFY (column datatype [DEFAULT expr]
[, Column datatype]…); Alter table table
Drop column column_name; alter table table_name rename columm old_column_name
TO new_column_name

Rename a table:
RENAME dept TO detail_dept;
Table renamed.

Delete table:
Drop table dept80;
Table dropped.

Clear table:
Truncate table detail_dept;
Table truncated.

These DDL languages cannot be rolled back and are automatically submitted.
You need to practice more to become familiar and proficient.