CREATE DATABASE

Function

Creates a database. By default, the new database will be created only by cloning the standard system database template0.

Precautions

• Only system administrators or users with the CREATEDB permission can create a database.
• CREATE DATABASE cannot be executed within a transaction block.
• During the database creation, an error message indicating that permission denied is displayed, possibly because the permission on the data directory in the file system is insufficient. If an error message, indicating no space left on device is displayed, the possible cause is that the disk space is used up.

Syntax

CreateDatabase ::= CREATE DATABASE [IF NOT EXISTS] database_name
    [ [ WITH ] { [ OWNER [=] user_name ] |
               [ TEMPLATE [=] template ] |
               [ ENCODING [=] encoding ] |
               [ LC_COLLATE [=] lc_collate ] |
               [ LC_CTYPE [=] lc_ctype ] |
               [ DBCOMPATIBILITY [=] compatibility_type ] |
               [ TABLESPACE [=] tablespace_name ] |
               [ CONNECTION LIMIT [=] connlimit ]}[...] ];

Parameter Description

• database_name

  Database name.

  Value range: String, which must comply with the naming convention.

• OWNER [ = ] user_name

  Specifies the owner of the new database. By default, the owner of a new database is the current user.

  Value range: an existing user name.

• TEMPLATE [ = ] template

  Specifies a template name, that is, the template from which the database is created. MogDB creates a database by copying data from a template database. MogDB has two default template databases template0 and template1 and a default user database postgres.

  Value range: template0

• ENCODING [ = ] encoding

  Specifies the encoding format used by the new database. The value can be a string (for example, SQL_ASCII) or an integer.

  By default, the encoding format of the template database is used. The encoding formats of the template databases template0 and template1 depend on the OS. The encoding format of template1 cannot be changed. If you need to change the encoding format when creating a database, use template0.

  Common values are GBK, UTF8, Latin1, and GB10830. The supported character sets are as follows:

  Table 1 MogDB character set

  Name	Description	Language	Server Or Not	ICU Or Not	Byte/Character	Alias
  BIG5	Big Five	Traditional Chinese	No	No	1-2	WIN950, Windows950
  EUC_CN	Extended UNIX Code-CN	Simplified Chinese	Yes	Yes	1-3	-
  EUC_JP	Extended UNIX Code-JP	Japanese	Yes	Yes	1-3	-
  EUC_JIS_2004	Extended UNIX Code-JP, JIS X 0213	Japanese	Yes	No	1-3	-
  EUC_KR	Extended UNIX Code-KR	Korean	Yes	Yes	1-3	-
  EUC_TW	Extended UNIX Code-Taiwan, China	Traditional Chinese	Yes	Yes	1-3	-
  GB18030	National Standard	Chinese	Yes	No	1-4	-
  GBK	Extended National Standard	Simplified Chinese	Yes	No	1-2	WIN936, Windows936
  ISO_8859_5	ISO 8859-5, ECMA 113	Latin/Cyrillic	Yes	Yes	1	-
  ISO_8859_6	ISO 8859-6, ECMA 114	Latin/Arabic	Yes	Yes	1	-
  ISO_8859_7	ISO 8859-7, ECMA 118	Latin/Greek	Yes	Yes	1	-
  ISO_8859_8	ISO 8859-8, ECMA 121	Latin/Hebrew	Yes	Yes	1	-
  JOHAB	JOHAB	Korean	No	No	1-3	-
  KOI8R	KOI8-R	Cyrillic (Russian)	Yes	Yes	1	KOI8
  KOI8U	KOI8-U	Cyrillic (Ukrainian)	Yes	Yes	1	-
  LATIN1	ISO 8859-1, ECMA 94	Western European	Yes	Yes	1	ISO88591
  LATIN2	ISO 8859-2, ECMA 94	Central European	Yes	Yes	1	ISO88592
  LATIN3	ISO 8859-3, ECMA 94	South European	Yes	Yes	1	ISO88593
  LATIN4	ISO 8859-4, ECMA 94	North European	Yes	Yes	1	ISO88594
  LATIN5	ISO 8859-9, ECMA 128	Turkish	Yes	Yes	1	ISO88599
  LATIN6	ISO 8859-10, ECMA 144	Nordic	Yes	Yes	1	ISO885910
  LATIN7	ISO 8859-13	Baltic	Yes	Yes	1	ISO885913
  LATIN8	ISO 8859-14	Celtic	Yes	Yes	1	ISO885914
  LATIN9	ISO 8859-15	LATIN1 with Euro and accents	Yes	Yes	1	ISO885915
  LATIN10	ISO 8859-16, ASRO SR 14111	Romanian	Yes	No	1	ISO885916
  MULE_INTERNAL	Mule internal code	Multilingual Emacs	Yes	No	1-4	-
  SJIS	Shift JIS	Japanese	No	No	1-2	Mskanji, ShiftJIS, WIN932, Windows932
  SHIFT_JIS_2004	Shift JIS, JIS X 0213	Japanese	No	No	1-2	-
  SQL_ASCII	Unspecified (see the text)	Any	Yes	No	1	-
  UHC	Unified Hangul Code	Korean	No	No	1-2	WIN949, Windows949
  UTF8	Unicode, 8-bit	All	Yes	Yes	1-4	Unicode
  WIN866	Windows CP866	Cyrillic	Yes	Yes	1	ALT
  WIN874	Windows CP874	Thai	Yes	No	1	-
  WIN1250	Windows CP1250	Central European	Yes	Yes	1	-
  WIN1251	Windows CP1251	Cyrillic	Yes	Yes	1	WIN
  WIN1252	Windows CP1252	Western European	Yes	Yes	1	-
  WIN1253	Windows CP1253	Greek	Yes	Yes	1	-
  WIN1254	Windows CP1254	Turkish	Yes	Yes	1	-
  WIN1255	Windows CP1255	Hebrew	Yes	Yes	1	-
  WIN1256	Windows CP1256	Arabic	Yes	Yes	1	-
  WIN1257	Windows CP1257	Baltic	Yes	Yes	1	-
  WIN1258	Windows CP1258	Vietnamese	Yes	Yes	1	ABC, TCVN, TCVN5712, VSCII

  CAUTION: Note that not all client APIs support the preceding character sets. The SQL_ASCII setting performs quite differently from other settings. If the character set of the server is SQL_ASCII, the server interprets the byte values 0 to 127 according to the ASCII standard. The byte values 128 to 255 are regarded as the characters that cannot be parsed. If this parameter is set to SQL_ASCII, no code conversion occurs. Therefore, this setting is not basically used to declare the specified encoding used, because this declaration ignores the encoding. In most cases, if you use any non-ASCII data, it is unwise to use the SQL_ASCII setting because MogDB will not be able to help you convert or validate non-ASCII characters.

  NOTICE:

  • The character set encoding of the new database must be compatible with the local settings (LC_COLLATE and LC_CTYPE).
  • When the specified character encoding set is GBK, some uncommon Chinese characters cannot be used directly as object names. This is because the byte encoding overlaps with the ASCII characters @A-Z[\]^_`a-z{|} when the second byte of the GBK ranges from 0x40 to 0x7E. @[\]^_'{|} is an operator in the database. If it is used directly as an object name, a syntax error will be reported. For example, the GBK hexadecimal code is 0x8240, and the second byte is 0x40, which is the same as the ASCII character @. Therefore, the character cannot be used as an object name. If you do need to use these characters, you can enclose them with double quotation marks ("") when creating and accessing objects to avoid this problem.
  • If the client encoding is A and the server encoding is B, the conversion between encoding formats A and B must exist in the database. For example: If the encoding format on the server is gb18030, the error message "Conversion between GB18030 and GBK is not supported." is displayed when you set the encoding format on the client to gbk because the current database does not support conversion between gb18030 and gbk. For details about all encoding formats supported by the database, see the pg_conversion system catalog.

• LC_COLLATE [ = ] lc_collate

  Specifies the character set used by the new database. For example, this parameter is set by running lc_collate = 'zh_CN.gbk'.

  The use of this parameter affects the sort order of strings (for example, the order of using ORDER BY for execution and the order of using indexes on text columns). The default is to use the collation order of the template database.

  Value range: A valid order type.

  Note: If you create a database with compatibility A, it is recommended to set lc_collate = 'C', otherwise it may lead to a difference in sorting results with the database you need to be compatible with. It is recommended to create a database with compatibility A using the following command.

  create database db1 DBCOMPATIBILITY='A' ENCODING='UTF8' LC_COLLATE='C' LC_CTYPE='C';

• LC_CTYPE [ = ] lc_ctype

  Specifies the character class used by the new database. For example, this parameter is set by running lc_ctype = 'zh_CN.gbk'. The use of this parameter affects the classification of characters, such as uppercase letters, lowercase letters, and digits. The default is to use the character classification of the template database.

  Value range: a valid character type

• DBCOMPATIBILITY [ = ] compatibility_type

  Specifies the compatible database type. The default compatible database is Oracle.

  Value range: A, B and PG, indicating Oracle, MySQL and Postgres databases, respectively.

  NOTE:

  • For A compatibility, the database treats empty strings as NULL and replaces DATE with TIMESTAMP(0) WITHOUT TIME ZONE.
  • When a character string is converted to an integer, if the input is invalid, the input will be converted to 0 due to B compatibility, and an error will be reported due to other compatibility issues.
  • For PG and MySQL compatibility, CHAR and VARCHAR are counted by character. For other compatibility types, they are counted by byte. For example, for the UTF-8 character set, CHAR(3) can store three Chinese characters in PG compatibility scenarios, but can store only one Chinese character in other compatibility scenarios.

• TABLESPACE [ = ] tablespace_name

  Specifies the name of the tablespace that will be associated with the new database.

  Value range: an existing tablespace name.

• CONNECTION LIMIT [ = ] connlimit

  Specifies the maximum number of concurrent connections that can be made to the new database.

  NOTICE:

  • This limit does not apply to sysadmin.
  • connlimit is calculated separately for each primary database node. Number of connections of the MogDB = connlimit x Number of normal CN master database nodes.

  Value range: An integer greater than or equal to -1. The default value -1 means no limit.

The restrictions on character encoding are as follows:

• If the locale is set to C (or POSIX), all encoding types are allowed. For other locale settings, the character encoding must be the same as that of the locale.
• If the character encoding mode is SQL_ASCII and the modifier is an administrator, the character encoding mode can be different from the locale setting.
• The encoding and region settings must match the template database, except that template0 is used as a template. This is because other databases might contain data that does not match the specified encoding, or might contain indexes whose sort ordering is affected by LC_COLLATE and LC_CTYPE. Copying such data will invalidate the indexes in the new database. template0 does not contain any data or indexes that may be affected.

Examples

-- Create users jim and tom.
MogDB=# CREATE USER jim PASSWORD 'xxxxxxxxx';
MogDB=# CREATE USER tom PASSWORD 'xxxxxxxxx';

-- Create database music using GBK (the local encoding type is also GBK).
MogDB=# CREATE DATABASE music ENCODING 'GBK' template = template0;

-- Create database music2 and specify jim as its owner.
MogDB=# CREATE DATABASE music2 OWNER jim;

-- Create database music3 using template template0 and specify jim as its owner.
MogDB=# CREATE DATABASE music3 OWNER jim TEMPLATE template0;

-- Set the maximum number of connections to database music to 10.
MogDB=# ALTER DATABASE music CONNECTION LIMIT= 10;

-- Rename database music to music4.
MogDB=# ALTER DATABASE music RENAME TO music4;

-- Change the owner of database music2 to tom.
MogDB=# ALTER DATABASE music2 OWNER TO tom;

-- Set the tablespace of database music3 to PG_DEFAULT.
MogDB=# ALTER DATABASE music3 SET TABLESPACE PG_DEFAULT;

-- Close the default index scan on database music3.
MogDB=# ALTER DATABASE music3 SET enable_indexscan TO off;

-- Reset parameter enable_indexscan.
MogDB=# ALTER DATABASE music3 RESET enable_indexscan;

-- Delete a database.
MogDB=# DROP DATABASE music2;
MogDB=# DROP DATABASE music3;
MogDB=# DROP DATABASE music4;

-- Delete users jim and tom.
MogDB=# DROP USER jim;
MogDB=# DROP USER tom;

-- Create a database compatible with the A format.
MogDB=# CREATE DATABASE ora_compatible_db DBCOMPATIBILITY 'A';

-- Delete the databases that are compatible with the A formats.
MogDB=# DROP DATABASE ora_compatible_db;

Helpful Links

ALTER DATABASE, DROP DATABASE

Optimization Suggestion

• create database

  Database cannot be created in a transaction.

• ENCODING LC_COLLATE LC_CTYPE

  If the new database Encoding, LC-Collate, or LC_Ctype does not match the template database (SQL_ASCII) ('GBK', 'UTF8', 'LATIN1', or 'GB18030'), template [=] template0 must be specified.