Temporary Tables - SQL Server to Aurora MySQL Migration Playbook
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Temporary Tables

Feature compatibility Amazon SCT / Amazon DMS automation level Amazon SCT action code index Key differences


                              Three star feature compatibility


                              Three star automation level

N/A

N/A

SQL Server Usage

SQL Server temporary tables are stored in the tempdb system database. There are two types of temporary tables: local and global. They differ from each other in their names, their visibility, and their availability. Local temporary tables have a single number sign # as the first character of their names; they are visible only to the current connection for the user, and they are deleted when the user disconnects from the instance of SQL Server.

Global temporary tables have two number signs ## as the first characters of their names; they are visible to any user after they are created, and they are deleted when all users referencing the table disconnect from the instance of SQL Server.

CREATE TABLE #MyTempTable (col1 INT PRIMARY KEY);

For more information, see Tables and Temporary Tables in the SQL Server documentation.

MySQL Usage

In MySQL, the table structure (DDL) of temporary tables isn’t stored in the database. When a session ends, the temporary table is dropped.

  • Session-Specific — In MySQL, each session is required to create its own temporary tables. Each session can create its own private temporary tables using identical table names.

  • In SQL Server, the default behavior when the ON COMMIT clause is omitted is ON COMMIT DELETE ROWS. In MySQL, the default is ON COMMIT PRESERVE ROWS and it can’t be changed.

Note

In Amazon Relational Database Service (Amazon RDS) for MySQL 8.0.13, user-created temporary tables and internal temporary tables created by the optimizer are stored in session temporary tablespaces that are allocated to a session from a pool of temporary tablespaces. When a session disconnects its temporary tablespaces are truncated and released back to the pool. In previous releases temporary tables were created in the ibtmp1 global temporary tablespace which did not return disk space to the operating system after temporary tables were dropped. The innodb_temp_tablespaces_dir variable defines the location where session temporary tablespaces are created. The default location is the #innodb_temp directory in the data directory. The INNODB_SESSION_TEMP_TABLESPACES table provides metadata about session temporary tablespaces. The ibtmp1 global temporary tablespace now stores rollback segments for changes made to user-created temporary tables.

Examples

CREATE TEMPORARY TABLE EMP_TEMP (
    EMP_ID INT PRIMARY KEY,
    EMP_FULL_NAME VARCHAR(60) NOT NULL,
    AVG_SALARY INT NOT NULL1;

Summary

Feature SQL Server Aurora MySQL

Semantic

Global temporary table

Temporary table

Create table

CREATE GLOBAL TEMPORARY…

CREATE TEMPORARY…

Accessible from multiple sessions

Yes

No

Temporary table DDL persist after session end or database restart user-managed datafiles

Yes

No (dropped at the end of the session)

Create index support

Yes

Yes

Foreign key support

Yes

Yes

ON COMMIT default

COMMIT DELETE ROWS

ON COMMIT PRESERVE ROWS

ON COMMIT PRESERVE ROWS

Yes

Yes

ON COMMIT DELETE ROWS

Yes

Yes

Alter table support

Yes

Yes

Gather statistics

dbms_stats.gather_table_stats

ANALYZE

Oracle 12c GLOBAL_TEMP_TABLE_STATS

dbms_stats.set_table_prefs

ANALYZE

For more information, see CREATE TEMPORARY TABLE Statement in the MySQL documentation.