Oracle temporary table explanation

One 、Oracle A temporary table

A temporary table is a special kind of table . When we need to （ It can be multiple ） When a batch of data in the table is operated repeatedly , Create a temporary table for this batch of data , May simplify operations and may improve efficiency ！

Basic grammar ：

create global temporary table  Temporary table name (
colum,colum,.......
)
on commit delete rows;
on commit preserve rows;

explain ：

• on commit delete rows; Indicates that the data row is only visible in the current transaction , It's also the default value , The data line will disappear after the transaction is committed ; A transaction level temporary table is created .
• on commit preserve rows; Indicates that data rows are visible only in the current session ; A session level temporary table is created .

Two 、 Demonstration of examples

2.1、 Transaction level temporary table

--  Create transaction level temporary tables  tmp_user  notes ：on commit delete rows  Omission 
create global temporary table tmp_user (
  user_id   varchar2(10),
  user_name varchar2(20)
) on commit delete rows;

2.2、 Session level temporary table

--  Create session level temporary tables  tmp_user1
create global temporary table tmp_user1 (
  user_id   varchar2(10),
  user_name varchar2(20)
)on commit preserve rows;

3、 ... and 、 Temporary table description

• The data of the temporary table is based on a session or a transaction , Other sessions cannot access .
• Temporary tables can be dedicated to transactions , It can also be dedicated to the session . For temporary tables dedicated to transaction processing , The data exists during the transaction ; For session specific temporary tables , Data exists during the session . In both cases , The data inserted by the session is dedicated to the session . Each session can only view and modify its own data . therefore , Data for temporary tables is never obtained DML lock