The document explains Oracle's Data Manipulation Language (DML) statements, which include insert, update, merge, and delete operations to manage data in databases. It discusses the concept of transactions, emphasizing their atomic nature and the significance of commit and rollback statements. Additionally, it highlights the difference between delete and truncate commands, particularly regarding how they affect the high water mark in database storage.

1. Oracle DML Statements
DML: Data Manipulation Language
Used to add, change or delete data
INSERT– add rows to a table
UPDATE – update existing rows in a table.
MERGE – update if rows exist, insert if they don’t
DELETE – delete rows from a table
http://adata.guru

2. Transactions
 A transaction is a sequence of SQL statements that Oracle Database treats as a single unit.
 Atomic unit of work that takes the database from one consistent state to another.
 Entire transaction succeeds or fails. No half-transactions.
 From the first DML statement to the first commit/rollback.
http://adata.guru

3. Transaction Control Statements
Commit
Ends your current transaction and make permanent all changes performed in the
transaction. Oracle Database issues an implicit COMMIT before and after any data
definition language (DDL) statement.
Rollback:
Undo work done in the current transaction. If you do not explicitly commit the
transaction and the program terminates abnormally, then Oracle Database rolls back
the last uncommitted transaction.
http://adata.guru

4. DML Statements – INSERT
 insert into <table_name> ( <column_names>)
Values (<column values>)
Insert into EMP (EMPNO,ENAME,JOB,MGR,HIREDATE,SAL,COMM,DEPTNO)
values (7369,'SMITH','CLERK',7902,to_date('17-DEC-1980','DD-MON-YYYY'),800,null,20);
 Insert into table_name ( < column names >)
{ select query }
Insert into locations (loc_name)
select loc
from scott.dept
union
select state_province
from hr.locations;
http://adata.guru

5. DML Statements – UPDATE
UPDATE <table_name>
SET <column-value-pairs>
WHERE <conditions>;
Update based on primary key:
UPDATE oe.customers
SET account_mgr_id = 149,
credit_limit = 3000
WHERE customer_id = 240;
Update a few rows based on a condition:
UPDATE oe.warehouses
SET warehouse_name = ‘Mumbai’
WHERE warehouse_name = ‘Bombay’;
No filter conditions.. Update all rows in the table.
UPDATE oe.customers
SET cust_email = upper(cust_email);
http://adata.guru

6. DML Statements – MERGE/UPSERT
MERGE into tgt_table
USING (source_table/source query)
ON <matching-conditions>
WHEN MATCHED then
update <column-value pairs>
WHEN NOT MATCHED then
INSERT <column-value pairs>
http://adata.guru

7. DML Statements – DELETE
Syntax :
DELETE from <table_name>
WHERE <conditions>;
Delete (one row) based on primary key:
DELETE from oe.customers
WHERE customer_id = 240;
DELETE a few rows based on a condition:
DELETE from oe.warehouses
WHERE warehouse_name = ‘Bombay’;
No filter conditions.. DELETE all rows in the table.
DELETE from oe.customers;
http://adata.guru

8. Delete v/s Truncate
http://adata.guru
HWM
HWM
HWM
HWM
HWM
Initial table creation. Full table scans are pretty
quick, since there are no blocks to scan
One million rows inserted (for example). High
water mark is advanced and oracle scans blocks
till HWM during a full scan. Inevitable.
Half a million rows deleted. HWM remains
unchanged, oracle still scans all the blocks during
a full table scan.
All rows are deleted using “delete” command.
HWM still at the same location, makes oracle still
do full table scans. Returns no data though.
TRUNCATE resets high water mark causing full-
scans and other operations to perform much
faster.