CREATE DATABASE in PostgreSQL

Postgres CREATE DATABASE

CREATE DATABASE creates a new PostgreSQL database.

You can create a database simply by this query:

CREATE DATABASE lusiadas;

//You'll see output like this 

//Messages

CREATE DATABASE

Query returned successfully in 1 secs 80 msec.

But that will be a database with default options.

By default, the new database will be created by cloning the standard system database template1.

A different template can be specified by writing TEMPLATE name. In particular, by writing TEMPLATE template0, you can create a virgin database containing only the standard objects predefined by your version of PostgreSQL. This is useful if you wish to avoid copying any installation-local objects that might have been added to template1.

There are ways to create customized database.

Syntax:

CREATE DATABASE name
    [ [ WITH ] [ OWNER [=] user_name ]
           [ TEMPLATE [=] template ]
           [ ENCODING [=] encoding ]
           [ LC_COLLATE [=] lc_collate ]
           [ LC_CTYPE [=] lc_ctype ]
           [ TABLESPACE [=] tablespace ]
           [ CONNECTION LIMIT [=] connlimit ] ]

Parameters in the syntax above

name: The name of a database to create.

user_name: The role name of the user who will own the new database, or DEFAULT to use the default (namely, the user executing the command).

To create a database owned by another role, you must be a direct or indirect member of that role, or be a superuser.

template: The name of the template from which to create the new database, or DEFAULT to use the default template (template1).

encoding: Character set encoding to use in the new database. Specify a string constant (e.g., ‘SQL_ASCII’), or an integer encoding number, or DEFAULT to use the default encoding (namely, the encoding of the template database). The character sets supported by the PostgreSQL server are described HERE.

lc_collate: Collation order (LC_COLLATE) to use in the new database. This affects the sort order applied to strings, e.g. in queries with ORDER BY, as well as the order used in indexes on text columns.

The default is to use the collation order of the template database. 

lc_ctype: Character classification (LC_CTYPE) to use in the new database. This affects the categorization of characters, e.g. lower, upper and digit.

The default is to use the character classification of the template database. 

tablespace: The name of the tablespace that will be associated with the new database, or DEFAULT to use the template database’s tablespace.

This tablespace will be the default tablespace used for objects created in this database. 

connlimit: How many concurrent connections can be made to this database. -1 (the default) means no limit.

CREATE DATABASE cannot be executed inside a transaction block.

More Examples

To create a database sales owned by user salesapp with a default tablespace of salesspace:

CREATE DATABASE sales OWNER salesapp TABLESPACE salesspace;

To create a database music which supports the ISO-8859-1 character set:

CREATE DATABASE music ENCODING 'LATIN1' TEMPLATE template0;

In this example, the TEMPLATE template0 clause would only be required if template1’s encoding is not ISO-8859-1. Note that changing encoding might require selecting new LC_COLLATE and LC_CTYPE settings as well.

Errors along the line of “could not initialize database directory” are most likely related to insufficient permissions on the data directory, a full disk, or other file system problems.

Although it is possible to copy a database other than template1 by specifying its name as the template, this is not (yet) intended as a general-purpose “COPY DATABASE” facility.

The principal limitation is that no other sessions can be connected to the template database while it is being copied.

CREATE DATABASE will fail if any other connection exists when it starts; otherwise, new connections to the template database are locked out until CREATE DATABASE completes. For more info CLICK HERE

The character set encoding specified for the new database must be compatible with the chosen locale settings (LC_COLLATE and LC_CTYPE).

If the locale is C (or equivalently POSIX), then all encodings are allowed, but for other locale settings there is only one encoding that will work properly. (On Windows, however, UTF-8 encoding can be used with any locale.)

CREATE DATABASE will allow superusers to specify SQL_ASCII encoding regardless of the locale settings, but this choice is deprecated and may result in misbehavior of character-string functions if data that is not encoding-compatible with the locale is stored in the database.

The encoding and locale settings must match those of the template database, except when template0 is used as 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 would result in a database that is corrupt according to the new settings. template0, however, is known to not contain any data or indexes that would be affected.

The CONNECTION LIMIT option is only enforced approximately; if two new sessions start at about the same time when just one connection “slot” remains for the database, it is possible that both will fail.

Also, the limit is not enforced against superusers.

Credit: Postgres Official Docs

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