When Does Oracle need commit.

Today, Oracle SQL plus performed the delete and query operations and then the query operations in PL/SQL. The results of the same statements were different, which made me feel quite depressed, later, I suddenly thought it may be caused by inconsistent data on both sides. But why is the inconsistency? Instead, I did not use commit. I checked it on the Internet, and I probably said this:

DML language, such as update, delete, insert, and so on, to modify data in a table, commit;
If the DDL language, such as create or drop, changes the table structure, you do not need to write commit (because commit is hidden internally );

DDL data definition language:
Create Table
ALTER TABLE
Drop table delete table
Truncate table delete all rows in the table
Create index create Index
Drop index Delete Index
When a DDL statement is executed, Oracle submits the current transaction before and after each statement. If you use the INSERT command to insert records into the database, a DDL Statement (such as create
In this case, data from the INSERT command will be submitted to the database. After a DDL statement is executed, it is automatically submitted and cannot be rolled back.

DML data operation language:
Insert inserts records into the database
Update and modify Database records
Delete Delete database records
If the DML command is not submitted, it will not be seen by other sessions. Unless the DDL or DCL command is executed after the DML command, or the user exits the session or terminates the instance, the system automatically
Issue the commit command to submit unsubmitted DML commands.

DDL:
Data Definition Language (DDL) statements are used to define the database structure or schema. Some examples:

Create-to create objects in the database

Alter-alters the structure of the database

Drop-delete objects from the database

Truncate-Remove all records from a table, including all spaces allocated for the records are removed

Comment-add comments to the data dictionary

Rename-Rename an object

DML:

Data manipulation language (DML) statements are used for managing data within schema objects. Some examples:

Select-retrieve data from the Database

Insert-insert data into a table

Update-updates existing data within a table

Delete-deletes all records from a table, the space for the records remain

Merge-upsert operation (insert or update)

Call-call a PL/SQL or Java Subprogram

Explain plan-explain access path to data

Lock table-control concurrency

DCL

Data Control Language (DCL) statements. Some examples:

Grant-gives user's access privileges to database

Revoke-withdraw access privileges given with the grant command

TCL

Transaction Control (TCL) statements are used to manage the changes made by DML statements. It allows statements to be grouped together into logical transactions.

Commit-save work done

Savepoint-identify a point in a transaction to which you can later roll back

Rollback-Restore database to original since the last commit

SET transaction-change transaction options like isolation level and what rollback segment to use