Appendix A Correspondence with Oracle Databases

This appendix explains the correspondence between PostgreSQL and Oracle databases.

A.1 Hint Clauses

Description

An execution plan specified for a query can be controlled per SQL statement by hints without any change in the settings for the entire server.

A.1.1 Hint Clause Correspondence

The table below lists the pg_hint_plan hints that correspond to Oracle database hints.

Correspondence between Oracle database hints and pg_hint_plan

Hint (Oracle database) Hint (PostgreSQL)
FIRST_ROWS hint Rows
FULL hint Seqscan
INDEX hint IndexScan
LEADING hint Leading
NO_INDEX hint NoIndexScan
NO_USE_HASH hint NoHashJoin
NO_USE_MERGE hint NoMergeJoin
NO_USE_NL hint NoNestLoop
ORDERED hint Leading
USE_HASH hint HashJoin
USE_MERGE hint MergeJoin
USE_NL hint NestLoop

Note

The optimizer operates differently for each database. Therefore, hint statements that are migrated as is may not have the same effect after migration. Be sure to verify operation at migration.

Migration example

The example below shows migration of a hint clause (INDEX hint).

Oracle database PostgreSQL 
SELECT /*+INDEX(inventory_table idx1)*/ *
 FROM inventory_table WHERE i_number = 110;
 
SELECT /*+IndexScan(inventory_table idx1)*/ *
 FROM inventory_table WHERE i_number = 110;

Note: The string idx1 is the index name defined for the i_number row of inventory_table.

Note

The pg_hint_plan hint, which is an extended feature of PostgreSQL, cannot be used to specify a column name or set a query block before the table name specification.

A.2 Dynamic Performance Views

Description

Dynamic performance views are views that can reference information mainly relating to database performance.

A.2.1 Alternatives for Dynamic Performance Views

PostgreSQL does not contain any dynamic performance views. Consider using the PostgreSQL system catalogs or statistics views instead.

The table below lists the alternative system catalogs and statistics views that correspond to the dynamic performance views.

Alternatives for dynamic performance views

Dynamic performance view
(Oracle database) 		System catalog or statistics view
(PostgreSQL)
V$ACCESS pg_locks
V$ACTIVE_SERVICES pg_stat_activity
V$ARCHIVED_LOG pg_stat_archiver
V$CLIENT_STATS pg_stat_activity
V$CONTEXT pg_settings
V$DATABASE pg_database
V$EMX_USAGE_STATS pg_stat_user_functions
V$ENABLEDPRIVS pg_authid
V$ENQUEUE_LOCK pg_locks
V$FILESTAT pg_statio_all_tables
V$FIXED_TABLE pg_views
V$FIXED_VIEW_DEFINITION pg_views
V$GES_BLOCKING_ENQUEUE pg_locks
V$GLOBAL_BLOCKED_LOCKS pg_locks
V$GLOBAL_TRANSACTION pg_locks
V$LOCK pg_locks
V$LOCKED_OBJECT pg_locks
V$MVREFRESH pg_matviews
V$MYSTAT pg_stat_all_tables or other view
V$NLS_PARAMETERS pg_settings
V$NLS_VALID_VALUES pg_proc
pg_ts_config
pg_collation
pg_type
V$OBJECT_PRIVILEGE pg_default_acl
V$OBJECT_USAGE pg_stat_all_indexes
V$OPEN_CURSOR pg_cursors
V$OPTION pg_settings
V$PARAMETER pg_settings
V$PARAMETER2 pg_settings
V$PROCESS pg_stat_activity
V$PWFILE_USERS pg_users
V$REPLPROP pg_replication_origin
pg_replication_origin_status
V$SESSION pg_stat_activity
V$SESSTAT pg_stat_all_tables or other view
V$SQLFN_METADATA pg_proc,pg_aggrgate
V$SYSTEM_PARAMETER pg_settings
V$SYSTEM_PARAMETER2 pg_settings
V$TABLESPACE pg_tablespace
V$TEMPSTAT pg_stat_database
V$TIMEZONE_NAMES pg_timezone_names
V$TRANSACTION pg_locks
V$TRANSACTION_ENQUEUE pg_locks

Note

Not all dynamic performance view information can be obtained from the system catalogs and statistics views. Each user should determine whether the obtained information can be used.

A.3 Formats

Description

Specifying formats in data type formatting functions makes it possible to convert numeric and date and time data types to formatted strings and to convert formatted strings to specific data types.

A.3.1 Number Format Correspondence

The table below indicates which Oracle database number formats are available in PostgreSQL.

Number format correspondence

Number format TO_CHAR TO_NUMBER Remarks
, (comma) Y Y
. (period) Y Y
$ YR YR If a dollar sign ($) is specified in any position other than the first character of a number format, move it to the front of the number format.
0 Y Y
9 Y Y
B Y Y
C N N
D Y Y
EEEE Y Y
G Y Y
L Y Y
MI Y Y
PR Y Y
RN Y -
Rn Y -
S Y Y
TM N -
U N N
V Y -
X N N
X N N

Y: Available

YR: Available with restrictions

N: Cannot be migrated

-: Does not need to be migrated (because it is not available in Oracle databases)

A.3.2 Datetime Format Correspondence

The table below indicates which Oracle database datetime formats are available in PostgreSQL.

Datetime format correspondence

Datetime format TO_CHAR TO_DATE TO_TIMESTAMP Remarks
-
/
,
.
;
:
"text" 		Y Y Y
AD Y Y Y
A.D. Y Y Y
AM Y Y Y
A.M. Y Y Y
BC Y Y Y
B.C. Y Y Y
CC Y - -
SCC Y - -
D Y Y Y
DAY Y Y Y
DD Y Y Y
DDD Y YR YR The year must also be specified. (This format is used together with other formats such as YYYY.)
DL N N N
DS N N N
DY Y Y Y
E N N N
EE N N N
FF1 to FF9 MR - MR Change to MS.
However, the number of digits is fixed at three.
FM YR YR YR Applies only to the format specified immediately after FM.
FX Y Y Y
HH Y Y Y
HH12 Y Y Y
HH24 Y Y Y
IW Y - -
IYYY Y - -
IYY Y - -
IY Y - -
I Y - -
J Y Y Y
MI Y Y Y
MM Y Y Y
MON Y Y Y
MONTH Y Y Y
PM Y Y Y
P.M. Y Y Y
Q Y - -
RM Y Y Y
RR Y Y Y
RRRR Y Y Y
SS Y Y Y
SSSSS M M M Change to SSSS.
TS N N N
TZD M - - Change to TZ.
TZH N - -
TZM N - -
TZR M - - Change to TZ.
WW Y Y Y
W Y Y Y
X Y - Y
Y,YYY Y Y Y
YEAR N - -
SYEAR N - -
YYYY Y Y Y
SYYYY N N N
YYY Y Y Y
YY Y Y Y
Y Y Y Y

Y: Available

M: Can be migrated

N: Cannot be migrated

YR: Available with restrictions

MR: Can be migrated with restrictions

-: Does not need to be migrated (because it is not available in Oracle databases)