Comparison of relational database management systems

The following tables compare general and technical information for a number of relational database management systems. Please see the individual products' articles for further information. Unless otherwise specified in footnotes, comparisons are based on the stable versions without any add-ons, extensions or external programs.

Operating system support

The operating systems that the RDBMSes can run on.

	Windows	macOS	Linux	BSD	UNIX	AmigaOS	z/OS	OpenVMS	iOS	Android
4th Dimension
ADABAS
Adaptive Server Enterprise
Advantage Database Server
Altibase
Apache Derby
ClustrixDB
CockroachDB
CUBRID
IBM Db2
Empress Embedded Database
EXASolution
FileMaker
Firebird
HSQLDB
H2
Informix Dynamic Server
Ingres
InterBase
Linter [SQL RDBMS]							Under Linux on IBM Z
LucidDB
MariaDB
MaxDB
Microsoft Access
Microsoft Visual Foxpro
Microsoft SQL Server
Microsoft SQL Server Compact (Embedded Database)
Mimer SQL
MonetDB
MySQL
Omnis Studio
OpenEdge
OpenLink Virtuoso
Oracle
Oracle Rdb
Actian Zen (PSQL)
Polyhedra
PostgreSQL							Under Linux on IBM Z
R:Base
SAP HANA
solidDB							Under Linux on IBM Z
SQL Anywhere
SQLBase
SQLite
SQream DB
Superbase
Superbase NG
Teradata
TiDB
UniData
UniVerse
YugabyteDB
	Windows	macOS	Linux	BSD	UNIX	AmigaOS	z/OS	OpenVMS	iOS	Android

Fundamental features

Information about what fundamental RDBMS features are implemented natively.

Database Name	ACID	Referential integrity	Transactions	Fine-grained locking	Multiversion concurrency control	Unicode	Interface	Type inference
4th Dimension							GUI & SQL
ADABAS							proprietary direct call & SQL
Adaptive Server Enterprise							API & GUI & SQL
Advantage Database Server						⁴	API & SQL
Altibase							API & GUI & SQL
Apache Derby							SQL
ClustrixDB							SQL
CockroachDB							SQL
CUBRID							GUI & SQL
IBM Db2							GUI & SQL
Empress Embedded Database							API & SQL
EXASolution							API & GUI & SQL
Firebird							API & SQL
HSQLDB							SQL
H2							SQL
Informix Dynamic Server							SQL, REST, MQ, and JSON
Ingres							SQL & QUEL
InterBase							SQL
Linter SQL RDBMS							API & GUI & SQL
LucidDB							SQL
MariaDB	²		² except for DDL				SQL
MaxDB							SQL
Microsoft Access							GUI & SQL
Microsoft Visual FoxPro							GUI & SQL
Microsoft SQL Server							GUI & SQL
Microsoft SQL Server Compact (Embedded Database)							GUI & SQL
Mimer SQL							API & GUI & SQL
MonetDB							API & SQL & MAL
MySQL	²	³	² except for DDL				GUI ⁵ & SQL
OpenEdge		⁶					GUI & SQL
OpenLink Virtuoso							API & GUI & SQL
Oracle			except for DDL				API & GUI & SQL
Oracle Rdb							SQL
Actian Zen (PSQL)							API & GUI & SQL
Polyhedra DBMS							API & SQL
PostgreSQL							API & GUI & SQL
SAP HANA							API & GUI & SQL
solidDB							API & SQL
SQL Anywhere							API & GUI & HTTP(S) & SQL
SQLBase							API & GUI & SQL
SQLite							API & SQL
Superbase NG							GUI & Proprietary & ODBC
Teradata							SQL
TiDB			except for DDL				GUI ⁵ & SQL
UniData							Multiple
UniVerse							Multiple
Database Name	ACID	Referential integrity	Transactions	Fine-grained locking	Multiversion concurrency control	Unicode	Interface	Type inference

Note (1): Currently only supports read uncommitted transaction isolation. Version [|1].[|9] adds serializable isolation and version [|2].0 will be fully ACID compliant.Note (2): MariaDB and MySQL provide ACID compliance through the default InnoDB storage engine.Note (3): "For other than InnoDB storage engines, MySQL Server parses and ignores the and syntax in statements." "The clause supports most core features for all storage engines."Note (4): Support for Unicode is new in version [|10].0.Note (5): MySQL provides GUI interface through MySQL Workbench.6 back|Note (6):] OpenEdge SQL database engine uses Referential Integrity, OpenEdge ABL Database engine does not and is handled via database triggers.

Limits

Information about data size limits.

	Max DB size	Max table size	Max row size	Max columns per row	Max Blob/Clob size	Max CHAR size	Max NUMBER size	Min DATE value	Max DATE value	Max column name size
4th Dimension	Limited			65,135	200 GB	200 GB	64 bits
Advantage Database Server	Unlimited	16 EiB		65,135 /	[\|4] GiB		64 bits			128
Apache Derby	Unlimited	Unlimited	Unlimited	1,012	2,147,483,647 chars	254	64 bits	0001-01-01	9999-12-31	128
ClustrixDB	Unlimited	Unlimited	64 MB on Appliance, 4 MB on AWS		64 MB	64 MB	64 MB	0001-01-01	9999-12-31	254
CUBRID	2 EB	2 EB	Unlimited	Unlimited	Unlimited	1 GB	64 bits	0001-01-01	9999-12-31	254
IBM DB2	Unlimited			1,012			64 bits	0001-01-01	9999-12-31	128
Empress Embedded Database	Unlimited	2⁶³−1 bytes	2 GB	32,767	2 GB	2 GB	64 bits	0000-01-01	9999-12-31	32
EXASolution	Unlimited	Unlimited	Unlimited	10,000		2 MB	128 bits	0001-01-01	9999-12-31	256
FileMaker	[\|8] TB	8 TB	8 TB	256,000,000	4 GB	10,000,000	1 billion characters, to, ±	0001-01-01	4000-12-31	100
Firebird	Unlimited¹	≈32 TB	65,536 B	Depends on data types used	32 GB	32,767 B	128 bits	100	32768	63
HSQLDB	64 TB	Unlimited⁸	Unlimited⁸	Unlimited⁸	64 TB⁷	Unlimited⁸	Unlimited⁸	0001-01-01	9999-12-31	128
H2	64 TB	Unlimited⁸	Unlimited⁸	Unlimited⁸	64 TB⁷	Unlimited⁸	64 bits	-99999999	99999999	Unlimited⁸
	Max DB size	Max table size	Max row size	Max columns per row	Max Blob/Clob size	Max CHAR size	Max NUMBER size	Min DATE value	Max DATE value	Max column name size
Informix Dynamic Server	≈0.[\|5] YB¹²	≈0,5YB¹²	32,765 bytes	32,765	4 TB	32,765¹⁴	10¹²⁵ ¹³	01/01/0001¹⁰	12/31/9999	128 bytes
Ingres	Unlimited	Unlimited	256 KB	1,024	2 GB	32 000 B	64 bits	0001	9999	256
InterBase	Unlimited¹	≈32 TB	65,536 B	Depends on data types used	2 GB	32,767 B	64 bits	100	32768	31
Linter SQL RDBMS	Unlimited	2³⁰ rows	64 KB, 2GB	250	2 GB	4000 B	64 bits	0001-01-01	9999-12-31	66
MariaDB	Unlimited	MyISAM storage limits: 256 TB; Innodb storage limits: 64 TB; Aria storage limits: ???	64 KB³	4,096⁴	4 GB	64 KB	64 bits	1000	9999	64
Microsoft Access	2 GB	2 GB	16 MB	255	64 KB, 1 GB	255 B	32 bits	0100	9999	64
Microsoft Visual Foxpro	Unlimited	2 GB	65,500 B	255	2 GB	16 MB	32 bits	0001	9999	10
Microsoft SQL Server	524,272 TB 16ZB per instance	524,272 TB	8,060 bytes / 2 TB⁶	1,024 / 30,000	2 GB / Unlimited	2 GB⁶	126 bits²	0001	9999	128
Microsoft SQL Server Compact (Embedded Database)	4 GB	4 GB	8,060 bytes	1024	2 GB	4000	154 bits	0001	9999	128
Mimer SQL	Unlimited	Unlimited	16000	252	Unlimited	15000	45 digits	0001-01-01	9999-12-31	128
MonetDB	Unlimited	Unlimited	Unlimited	Unlimited	2 GB	2 GB	128 bits	-4712-01-01	9999-12-31	1024
MySQL	Unlimited	MyISAM storage limits: 256 TB; Innodb storage limits: 64 TB	64 KB³	4,096⁴	4 GB	64 KB	64 bits	1000	9999	64
OpenLink Virtuoso	32 TB per instance	DB size	4 KB	200	2 GB	2 GB	2³¹	0	9999	100
Oracle		4 GB × block size	8 KB	1,000	128 TB	32,767 B¹¹	126 bits	−4712	9999	128
	Max DB size	Max table size	Max row size	Max columns per row	Max Blob/Clob size	Max CHAR size	Max NUMBER size	Min DATE value	Max DATE value	Max column name size
Actian Zen (PSQL)	4 billion objects	256 GB	2 GB	1,536	2 GB	8,000 bytes	64 bits	01-01-0001	12-31-9999	128 bytes
Polyhedra	Limited by available RAM, address space	2³² rows	Unlimited	65,536	4 GB	4 GB	64 bits	0001-01-01	8000-12-31	255
PostgreSQL	Unlimited	32 TB	1.6 TB	250–1600 depending on type	1 GB stored inline or 4 TB using pg_largeobject	1 GB	Unlimited	−4,713	5,874,897	63
SAP HANA
solidDB	256 TB	256 TB	32 KB + BLOB data	Limited by row size	4 GB	4 GB	64 bits	-32768-01-01	32767-12-31	254
SQL Anywhere	104 TB	Limited by file size	Limited by file size	45,000	2 GB	2 GB	64 bits	0001-01-01	9999-12-31	128 bytes
SQLite	128 TB	Limited by file size	Limited by file size	32,767	2 GB	2 GB	64 bits	No DATE type⁹	No DATE type⁹	Unlimited
Teradata	Unlimited	Unlimited	64000 wo/lobs	2,048	2 GB	64,000	38 digits	0001-01-01	9999-12-31	128
UniVerse	Unlimited	Unlimited	Unlimited	Unlimited	Unlimited	Unlimited	Unlimited	Unlimited	Unlimited	Unlimited
	Max DB size	Max table size	Max row size	Max columns per row	Max Blob/Clob size	Max CHAR size	Max NUMBER size	Min DATE value	Max DATE value	Max column name size

Note (1): Firebird 2.x maximum database size is effectively unlimited with the largest known database size >980 GB. Firebird 1.5.x maximum database size: 32 TB.Note (2): Limit is 10³⁸ using DECIMAL datatype.Note (3): InnoDB is limited to 8,000 bytes.Note (4): InnoDB is limited to 1,017 columns.Note (6): Using VARCHAR in SQL 2005 and later.Note (7): When using a page size of 32 KB, and when BLOB/CLOB data is stored in the database file.Note (8): Java array size limit of 2,147,483,648 objects per array applies. This limit applies to number of characters in names, rows per table, columns per table, and characters per CHAR/VARCHAR.Note (9): Despite the lack of a date datatype, SQLite does include date and time functions, which work for timestamps between 24 November 4714 B.C. and 1 November 5352.Note (10): Informix DATETIME type has adjustable range from YEAR only through 1/10000th second. DATETIME date range is 0001-01-01 00:00:00.00000 through 9999-12-31 23:59:59.99999.Note (11): Since version 12c. Earlier versions support up to.Note (12): The limit refers to the storage limit of a single Informix server instance beginning with v15.0. Informix v12.10 and later versions support using sharding techniques to distribute a table across multiple server instances. A distributed Informix database has no upper limit on table or database size.Note (13): Informix DECIMAL type supports up to 32 decimal digits of precision with a range of to. Fixed and variable precision are supported.Note (14): The LONGLVARCHAR type supports strings up to 4TB.

Tables and views

Information about what tables and views are supported natively.

	Temporary table	Materialized view
4th Dimension
ADABAS
Adaptive Server Enterprise	¹	– see precomputed result sets
Advantage Database Server
Altibase
Apache Derby
ClustrixDB
CUBRID
IBM Db2
Empress Embedded Database
EXASolution
Firebird
HSQLDB
H2
Informix Dynamic Server		²
Ingres
InterBase
Linter SQL RDBMS
LucidDB
MariaDB		⁴
MaxDB
Microsoft Access
Microsoft Visual Foxpro
Microsoft SQL Server
Microsoft SQL Server Compact (Embedded Database)
Mimer SQL
MonetDB
MySQL		⁴
Oracle
Oracle Rdb
OpenLink Virtuoso
Actian Zen (PSQL)
Polyhedra DBMS
PostgreSQL
SAP HANA
solidDB
SQL Anywhere
SQLite
Superbase
Teradata
UniData
UniVerse
	Temporary table	Materialized view

Note (1): Server provides tempdb, which can be used for public and private temp tables.Note (2): Materialized views are not supported in Informix; the term is used in IBM's documentation to refer to a temporary table created to run the view's query when it is too complex, but one cannot for example define the way it is refreshed or build an index on it. The term is defined in the Informix Performance Guide.Note (4): Materialized views can be emulated using stored procedures and triggers.

Indexes

Information about what indexes are supported natively.

Forest of Trees Index

Duplicate index prevention

4th Dimension

Cluster

ADABAS

Adaptive Server Enterprise

Advantage Database Server

Empress Embedded Database

EXASolution

Firebird

HSQLDB

Informix Dynamic Server

Ingres

InterBase

Linter SQL RDBMS¹⁰

temporary indexes for equality joins

for some scalar functions like LOWER and UPPER

LucidDB

MariaDB

Aria and MyISAM tables and, since v10.2.2, InnoDB tables only

MEMORY, InnoDB,⁵ tables only

PERSISTENT virtual columns only

Aria and MyISAM tables and, since v10.2.2, InnoDB tables only

MaxDB

Microsoft Access

Microsoft Visual Foxpro

Microsoft SQL Server

Spatial Indexes

⁴

on Computed columns³

Bitmap filter index for Star Join Query

Microsoft SQL Server Compact (Embedded Database)

Mimer SQL

MonetDB

MySQL

Spatial Indexes

MEMORY, Cluster, InnoDB,⁵ tables only

MyISAM tables and, since v5.6.4, InnoDB tables

MyISAM tables and, since v5.7.5, InnoDB tables

OpenLink Virtuoso

Cluster

Oracle

¹¹

Cluster Tables

⁶

⁷

PostGIS

SpatiaLite

Forest of Trees Index

Duplicate index prevention

Note (1): The users need to use a function from freeAdhocUDF library or similar.Note (2): Can be implemented for most data types using expression-based indexes.Note (3): Can be emulated by indexing a computed column or by using an "Indexed View".Note (4): Used for InMemory ColumnStore index, temporary hash index for hash join, Non/Cluster & fill factor.Note (5): InnoDB automatically generates adaptive hash index entries as needed.Note (6): Can be implemented using Function-based Indexes in Oracle 8i and higher, but the function needs to be used in the sql for the index to be used.Note (7): A PostgreSQL functional index can be used to reverse the order of a field.Note (10): B+ tree and full-text only for now.Note (11): R-Tree indexing available in base edition with Locator but some functionality requires Personal Edition or Enterprise Edition with Spatial option.Note (12): FOT or Forest of Trees indexes is a type of B-tree index consisting of multiple B-trees which reduces contention in multi-user environments.

Database capabilities

Note (1): Recursive CTEs introduced in 11gR2 supersedes similar construct called CONNECT BY.

Data types

	Type system	Integer	Floating point	Decimal	String	Binary	Date/Time	Boolean	Other
4th Dimension	Static	,,,,	,	,	,,	,,	,,
Altibase	Static	,,	,	,,,	,,,,	,,,,
ClustrixDB	Static	,,,,	,		,,,,,,,	,,,	,,,	,	,,
CUBRID	Static	,,	,,	,	,,,,		,,,		,,,,,
IBM Db2		,,	,,		,,	,,	,,,		,,,,
Empress Embedded Database	Static	,, or ;,, or ;,,, or ;,, or	,, or ;,, or ;, or ;	,,,, or ;	,,,,,,,,,	or ;	,,,,,,		32,
EXASolution	Static	,,,,	,,	,,,	,,,,,,,		,,	,
FileMaker	Static
Firebird		,,,	,	,,,	,,,,	,	,,		,,, User defined types
	Type system	Integer	Floating point	Decimal	String	Binary	Date/Time	Boolean	Other
HSQLDB	Static	,,,		,	,,,	,,,	,,,		,,,
Informix Dynamic Server	Static +	,,,	,	,	,,,,,,,	,,,	,,		,,,,,,,,,,
Ingres	Static	,,,	,		C,,,,,,,	,,	,,,,,		,,, -
Linter SQL RDBMS	Static + Dynamic	,,	,	,	,,,,	,,			,
MariaDB	Static	,,,,	,		,,,,,,,	,,,	,,,	, = synonym for	,, data types
Microsoft SQL Server	Static	,,,	,	,,,	,,,,,	,,,,	,,,,,		,,,,,,, Geometry, Geography, Custom.NET datatypes
Microsoft SQL Server Compact (Embedded Database)	Static	,,,	,	,,	,,	,,			,,,,
Mimer SQL	Static	,,,	,,,	,	,,,,,	,,	,,,		,
MonetDB	Static, extensible	,,,,,,,	,,,,	,	,,,,,,,	,	,,,,,,,,,,		,,,,,, data types, User Defined Types
MySQL	Static	,,,,	,		,,,,,,,	,,,	,,,	, = synonym for	,, data types
OpenLink Virtuoso	Static + Dynamic	,,	,,,	,,,,,	,,,,,		,,,		,,,
	Type system	Integer	Floating point	Decimal	String	Binary	Date/Time	Boolean	Other
Oracle	Static + Dynamic		,		,,,,,,	,,,	,,		,,,,, XMLType,,
Actian Zen (PSQL)	Static	,,,,,,,	,,,	,,,,,,	,,	,,	,,		,,,,
Polyhedra	Static	,,,	,		,
PostgreSQL	Static	,,	,	,	,,		,,,		,,,,,,,,,,,,,,,, arrays, composites, ranges, custom
SAP HANA	Static	,,,	,,,,		,,,	,,	,,,		,,,,,,,,,,,,
solidDB	Static	,,,	,,	,	,,,,,	,,	,,
SQLite	Dynamic
SQream DB	Static	,,,	,		,,		,
	Type system	Integer	Floating point	Decimal	String	Binary	Date/Time	Boolean	Other
Teradata	Static	,,,		,	,,	,,	,,		,,,,,
UniData	Dynamic
UniVerse	Dynamic
	Type system	Integer	Floating point	Decimal	String	Binary	Date/Time	Boolean	Other

Other objects

Information about what other objects are supported natively.

	Data domain	Cursor	Trigger	Function¹	Procedure¹	External routine¹
4th Dimension
ADABAS				?	?
Adaptive Server Enterprise
Advantage Database Server
Altibase
Apache Derby				²	²	²
ClustrixDB
CUBRID					²
Empress Embedded Database	via RANGE CHECK
EXASolution
IBM Db2	via CHECK CONSTRAINT
Firebird
HSQLDB
H2			²	²	²
Informix Dynamic Server	via CHECK					⁵
Ingres
InterBase
Linter SQL RDBMS
LucidDB				²	²	²
MariaDB
MaxDB
Microsoft Access
Microsoft Visual Foxpro
Microsoft SQL Server
Microsoft SQL Server Compact (Embedded Database)
Mimer SQL
MonetDB
MySQL	³
Oracle
Oracle Rdb
OpenLink Virtuoso
Actian Zen (PSQL)
Polyhedra DBMS
PostgreSQL
SAP HANA
solidDB
SQL Anywhere
SQLite
Teradata
UniData
UniVerse
	Data domain	Cursor	Trigger	Function¹	Procedure¹	External routine¹

Note (1): Both function and procedure refer to internal routines written in SQL and/or procedural language like PL/SQL. External routine refers to the one written in the host languages, such as C, Java, Cobol, etc. "Stored procedure" is a commonly used term for these routine types. However, its definition varies between different database vendors.Note (2): In Derby, H2, LucidDB, and CUBRID, users code functions and procedures in Java.Note (3): ENUM datatype exists. CHECK clause enforced as of 8.0.16.Note (5): Informix supports external functions written in Java, C, & C++.

Partitioning

Information about what partitioning methods are supported natively.

	Range	Hash	Composite	List	Expression	Round Robin
4th Dimension
ADABAS
Adaptive Server Enterprise
Advantage Database Server
Altibase
Apache Derby
ClustrixDB
CUBRID
IBM Db2
Empress Embedded Database
EXASolution
Firebird
HSQLDB
H2
Informix Dynamic Server
Ingres
InterBase
Linter SQL RDBMS
MariaDB
MaxDB
Microsoft Access
Microsoft Visual Foxpro
Microsoft SQL Server
Microsoft SQL Server Compact (Embedded Database)
Mimer SQL
MonetDB
MySQL
Oracle
Oracle Rdb
OpenLink Virtuoso
Actian Zen (PSQL)
Polyhedra DBMS
PostgreSQL
SAP HANA
solidDB
SQL Anywhere
SQLite
Teradata
UniVerse
	Range	Hash	Composite	List	Expression	Round Robin

Access control

Information about access control functionalities.

	Native network encryption¹	Brute-force protection	Enterprise directory compatibility	Password complexity rules²	Patch access³	Run unprivileged⁴	Audit
4D
Adaptive Server Enterprise
Advantage Database Server
CUBRID
IBM Db2
Empress Embedded Database
EXASolution
Firebird								⁷
HSQLDB
H2
Informix Dynamic Server			¹⁰	¹⁰
Linter SQL RDBMS
MariaDB								⁸
Microsoft SQL Server
Microsoft SQL Server Compact (Embedded Database)
Mimer SQL
MySQL								⁸
OpenLink Virtuoso
Oracle
Actian Zen (PSQL)							¹²
Polyhedra DBMS							¹³	¹³
PostgreSQL
SAP HANA
solidDB
SQL Anywhere
SQLite
Teradata
	Native network encryption¹	Brute-force protection	Enterprise directory compatibility	Password complexity rules²	Patch access³	Run unprivileged⁴	Audit

Note (1): Network traffic could be transmitted in a secure way. Precise if option is default, included option or an extra modules to buy.Note (2): Options are present to set a minimum size for password, respect complexity like presence of numbers or special characters.Note (3): How do you get security updates? Is it free access, do you need a login or to pay? Is there easy access through a Web/FTP portal or RSS feed or only through offline access.Note (4): Does database process run as root/administrator or unprivileged user? What is default configuration?Note (5): Is there a separate user to manage special operation like backup, security officer, administrator, etc.? Is it default or optional?Note (6): Common Criteria certified product list.Note (7): FirebirdSQL seems to only have SYSDBA user and DB owner. There are no separate roles for backup operator and security administrator.Note (8): User can define a dedicated backup user but nothing particular in default install.Note (9): Authentication methods.Note (10): Informix Dynamic Server supports PAM and other configurable authentication. By default uses OS authentication.Note (11): Authentication methods.Note (12): With the use of Pervasive AuditMaster.Note (13): User-based security is optional in Polyhedra, but when enabled can be enhanced to a role-based model with auditing.

Databases vs schemas (terminology)

The SQL specification defines what an "SQL schema" is; however, databases implement it differently. To compound this confusion the functionality can overlap with that of a parent database. An SQL schema is simply a namespace within a database; things within this namespace are addressed using the member operator dot "". This seems to be a universal among all of the implementations.
A true fully (database, schema, and table) qualified query is exemplified as such:
Both a schema and a database can be used to isolate one table, "foo", from another like-named table "foo". The following is pseudo code:

The problem that arises is that former MySQL users will create multiple databases for one project. In this context, MySQL databases are analogous in function to PostgreSQL-schemas, insomuch as PostgreSQL deliberately lacks off-the-shelf cross-database functionality that MySQL has. Conversely, PostgreSQL has applied more of the specification implementing cross-table, cross-schema, and then left room for future cross-database functionality.
MySQL aliases schema with database behind the scenes, such that and are analogs. It can therefore be said that MySQL has implemented cross-database functionality, skipped schema functionality entirely, and provided similar functionality into their implementation of a database. In summary, PostgreSQL fully supports schemas and multi-tenancy by strictly separating databases from each other and thus lacks some functionality MySQL has with databases, while MySQL does not even attempt to support standard schemas.
Oracle has its own spin where creating a user is synonymous with creating a schema. Thus a database administrator can create a user called PROJECT and then create a table PROJECT.TABLE. Users can exist without schema objects, but an object is always associated with an owner. With the 'shared-everything' Oracle RAC architecture, the same database can be opened by multiple servers concurrently. This is independent of replication, which can also be used, whereby the data is copied for use by different servers. In the Oracle implementation, a 'database' is a set of files which contains the data while the 'instance' is a set of processes through which a database is accessed.
Informix supports multiple databases in a server instance like MySQL. It supports the syntax as a way to group DDL statements into a single unit creating all objects created as a part of the schema as a single owner. Informix supports a database mode called ANSI mode which supports creating objects with the same name but owned by different users.
PostgreSQL and some other databases have support for foreign schemas, which is the ability to import schemas from other servers as defined in ISO/IEC 9075-9. This appears like any other schema in the database according to the SQL specification while accessing data stored either in a different database or a different server instance. The import can be made either as an entire foreign schema or merely certain tables belonging to that foreign schema. While support for ISO/IEC 9075-9 bridges the gap between the two competing philosophies surrounding schemas, MySQL and Informix maintain an implicit association between databases while ISO/IEC 9075-9 requires that any such linkages be explicit in nature.