Baoding-FenShuaJiang
/
Green_GoodERP18_FSJ_Standard


			
				
					
						
						
							
							<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>5.9. Schemas</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="prev" href="ddl-rowsecurity.html" title="5.8. Row Security Policies" /><link rel="next" href="ddl-inherit.html" title="5.10. Inheritance" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">5.9. Schemas</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="ddl-rowsecurity.html" title="5.8. Row Security Policies">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="ddl.html" title="Chapter 5. Data Definition">Up</a></td><th width="60%" align="center">Chapter 5. Data Definition</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="ddl-inherit.html" title="5.10. Inheritance">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="DDL-SCHEMAS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">5.9. Schemas</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="ddl-schemas.html#DDL-SCHEMAS-CREATE">5.9.1. Creating a Schema</a></span></dt><dt><span class="sect2"><a href="ddl-schemas.html#DDL-SCHEMAS-PUBLIC">5.9.2. The Public Schema</a></span></dt><dt><span class="sect2"><a href="ddl-schemas.html#DDL-SCHEMAS-PATH">5.9.3. The Schema Search Path</a></span></dt><dt><span class="sect2"><a href="ddl-schemas.html#DDL-SCHEMAS-PRIV">5.9.4. Schemas and Privileges</a></span></dt><dt><span class="sect2"><a href="ddl-schemas.html#DDL-SCHEMAS-CATALOG">5.9.5. The System Catalog Schema</a></span></dt><dt><span class="sect2"><a href="ddl-schemas.html#DDL-SCHEMAS-PATTERNS">5.9.6. Usage Patterns</a></span></dt><dt><span class="sect2"><a href="ddl-schemas.html#DDL-SCHEMAS-PORTABILITY">5.9.7. Portability</a></span></dt></dl></div><a id="id-1.5.4.11.2" class="indexterm"></a><p>
   A <span class="productname">PostgreSQL</span> database cluster contains
   one or more named databases.  Roles and a few other object types are
   shared across the entire cluster.  A client connection to the server
   can only access data in a single database, the one specified in the
   connection request.
  </p><div class="note"><h3 class="title">Note</h3><p>
    Users of a cluster do not necessarily have the privilege to access every
    database in the cluster.  Sharing of role names means that there
    cannot be different roles named, say, <code class="literal">joe</code> in two databases
    in the same cluster; but the system can be configured to allow
    <code class="literal">joe</code> access to only some of the databases.
   </p></div><p>
   A database contains one or more named <em class="firstterm">schemas</em>, which
   in turn contain tables.  Schemas also contain other kinds of named
   objects, including data types, functions, and operators.  The same
   object name can be used in different schemas without conflict; for
   example, both <code class="literal">schema1</code> and <code class="literal">myschema</code> can
   contain tables named <code class="literal">mytable</code>.  Unlike databases,
   schemas are not rigidly separated: a user can access objects in any
   of the schemas in the database they are connected to, if they have
   privileges to do so.
  </p><p>
   There are several reasons why one might want to use schemas:

   </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
      To allow many users to use one database without interfering with
      each other.
     </p></li><li class="listitem"><p>
      To organize database objects into logical groups to make them
      more manageable.
     </p></li><li class="listitem"><p>
      Third-party applications can be put into separate schemas so
      they do not collide with the names of other objects.
     </p></li></ul></div><p>

   Schemas are analogous to directories at the operating system level,
   except that schemas cannot be nested.
  </p><div class="sect2" id="DDL-SCHEMAS-CREATE"><div class="titlepage"><div><div><h3 class="title">5.9.1. Creating a Schema</h3></div></div></div><a id="id-1.5.4.11.7.2" class="indexterm"></a><p>
    To create a schema, use the <a class="xref" href="sql-createschema.html" title="CREATE SCHEMA"><span class="refentrytitle">CREATE SCHEMA</span></a>
    command.  Give the schema a name
    of your choice.  For example:
</p><pre class="programlisting">
CREATE SCHEMA myschema;
</pre><p>
   </p><a id="id-1.5.4.11.7.4" class="indexterm"></a><a id="id-1.5.4.11.7.5" class="indexterm"></a><p>
    To create or access objects in a schema, write a
    <em class="firstterm">qualified name</em> consisting of the schema name and
    table name separated by a dot:
</p><pre class="synopsis">
<em class="replaceable"><code>schema</code></em><code class="literal">.</code><em class="replaceable"><code>table</code></em>
</pre><p>
    This works anywhere a table name is expected, including the table
    modification commands and the data access commands discussed in
    the following chapters.
    (For brevity we will speak of tables only, but the same ideas apply
    to other kinds of named objects, such as types and functions.)
   </p><p>
    Actually, the even more general syntax
</p><pre class="synopsis">
<em class="replaceable"><code>database</code></em><code class="literal">.</code><em class="replaceable"><code>schema</code></em><code class="literal">.</code><em class="replaceable"><code>table</code></em>
</pre><p>
    can be used too, but at present this is just for <span class="foreignphrase"><em class="foreignphrase">pro
    forma</em></span> compliance with the SQL standard.  If you write a database name,
    it must be the same as the database you are connected to.
   </p><p>
    So to create a table in the new schema, use:
</p><pre class="programlisting">
CREATE TABLE myschema.mytable (
 ...
);
</pre><p>
   </p><a id="id-1.5.4.11.7.9" class="indexterm"></a><p>
    To drop a schema if it's empty (all objects in it have been
    dropped), use:
</p><pre class="programlisting">
DROP SCHEMA myschema;
</pre><p>
    To drop a schema including all contained objects, use:
</p><pre class="programlisting">
DROP SCHEMA myschema CASCADE;
</pre><p>
    See <a class="xref" href="ddl-depend.html" title="5.14. Dependency Tracking">Section 5.14</a> for a description of the general
    mechanism behind this.
   </p><p>
    Often you will want to create a schema owned by someone else
    (since this is one of the ways to restrict the activities of your
    users to well-defined namespaces).  The syntax for that is:
</p><pre class="programlisting">
CREATE SCHEMA <em class="replaceable"><code>schema_name</code></em> AUTHORIZATION <em class="replaceable"><code>user_name</code></em>;
</pre><p>
    You can even omit the schema name, in which case the schema name
    will be the same as the user name.  See <a class="xref" href="ddl-schemas.html#DDL-SCHEMAS-PATTERNS" title="5.9.6. Usage Patterns">Section 5.9.6</a> for how this can be useful.
   </p><p>
    Schema names beginning with <code class="literal">pg_</code> are reserved for
    system purposes and cannot be created by users.
   </p></div><div class="sect2" id="DDL-SCHEMAS-PUBLIC"><div class="titlepage"><div><div><h3 class="title">5.9.2. The Public Schema</h3></div></div></div><a id="id-1.5.4.11.8.2" class="indexterm"></a><p>
    In the previous sections we created tables without specifying any
    schema names.  By default such tables (and other objects) are
    automatically put into a schema named <span class="quote">“<span class="quote">public</span>”</span>.  Every new
    database contains such a schema.  Thus, the following are equivalent:
</p><pre class="programlisting">
CREATE TABLE products ( ... );
</pre><p>
    and:
</p><pre class="programlisting">
CREATE TABLE public.products ( ... );
</pre><p>
   </p></div><div class="sect2" id="DDL-SCHEMAS-PATH"><div class="titlepage"><div><div><h3 class="title">5.9.3. The Schema Search Path</h3></div></div></div><a id="id-1.5.4.11.9.2" class="indexterm"></a><a id="id-1.5.4.11.9.3" class="indexterm"></a><a id="id-1.5.4.11.9.4" class="indexterm"></a><p>
    Qualified names are tedious to write, and it's often best not to
    wire a particular schema name into applications anyway.  Therefore
    tables are often referred to by <em class="firstterm">unqualified names</em>,
    which consist of just the table name.  The system determines which table
    is meant by following a <em class="firstterm">search path</em>, which is a list
    of schemas to look in.  The first matching table in the search path
    is taken to be the one wanted.  If there is no match in the search
    path, an error is reported, even if matching table names exist
    in other schemas in the database.
   </p><p>
    The ability to create like-named objects in different schemas complicates
    writing a query that references precisely the same objects every time.  It
    also opens up the potential for users to change the behavior of other
    users' queries, maliciously or accidentally.  Due to the prevalence of
    unqualified names in queries and their use
    in <span class="productname">PostgreSQL</span> internals, adding a schema
    to <code class="varname">search_path</code> effectively trusts all users having
    <code class="literal">CREATE</code> privilege on that schema.  When you run an
    ordinary query, a malicious user able to create objects in a schema of
    your search path can take control and execute arbitrary SQL functions as
    though you executed them.
   </p><a id="id-1.5.4.11.9.7" class="indexterm"></a><p>
    The first schema named in the search path is called the current schema.
    Aside from being the first schema searched, it is also the schema in
    which new tables will be created if the <code class="command">CREATE TABLE</code>
    command does not specify a schema name.
   </p><a id="id-1.5.4.11.9.9" class="indexterm"></a><p>
    To show the current search path, use the following command:
</p><pre class="programlisting">
SHOW search_path;
</pre><p>
    In the default setup this returns:
</p><pre class="screen">
 search_path
--------------
 "$user", public
</pre><p>
    The first element specifies that a schema with the same name as
    the current user is to be searched.  If no such schema exists,
    the entry is ignored.  The second element refers to the
    public schema that we have seen already.
   </p><p>
    The first schema in the search path that exists is the default
    location for creating new objects.  That is the reason that by
    default objects are created in the public schema.  When objects
    are referenced in any other context without schema qualification
    (table modification, data modification, or query commands) the
    search path is traversed until a matching object is found.
    Therefore, in the default configuration, any unqualified access
    again can only refer to the public schema.
   </p><p>
    To put our new schema in the path, we use:
</p><pre class="programlisting">
SET search_path TO myschema,public;
</pre><p>
    (We omit the <code class="literal">$user</code> here because we have no
    immediate need for it.)  And then we can access the table without
    schema qualification:
</p><pre class="programlisting">
DROP TABLE mytable;
</pre><p>
    Also, since <code class="literal">myschema</code> is the first element in
    the path, new objects would by default be created in it.
   </p><p>
    We could also have written:
</p><pre class="programlisting">
SET search_path TO myschema;
</pre><p>
    Then we no longer have access to the public schema without
    explicit qualification.  There is nothing special about the public
    schema except that it exists by default.  It can be dropped, too.
   </p><p>
    See also <a class="xref" href="functions-info.html" title="9.25. System Information Functions and Operators">Section 9.25</a> for other ways to manipulate
    the schema search path.
   </p><p>
    The search path works in the same way for data type names, function names,
    and operator names as it does for table names.  Data type and function
    names can be qualified in exactly the same way as table names.  If you
    need to write a qualified operator name in an expression, there is a
    special provision: you must write
</p><pre class="synopsis">
<code class="literal">OPERATOR(</code><em class="replaceable"><code>schema</code></em><code class="literal">.</code><em class="replaceable"><code>operator</code></em><code class="literal">)</code>
</pre><p>
    This is needed to avoid syntactic ambiguity.  An example is:
</p><pre class="programlisting">
SELECT 3 OPERATOR(pg_catalog.+) 4;
</pre><p>
    In practice one usually relies on the search path for operators,
    so as not to have to write anything so ugly as that.
   </p></div><div class="sect2" id="DDL-SCHEMAS-PRIV"><div class="titlepage"><div><div><h3 class="title">5.9.4. Schemas and Privileges</h3></div></div></div><a id="id-1.5.4.11.10.2" class="indexterm"></a><p>
    By default, users cannot access any objects in schemas they do not
    own.  To allow that, the owner of the schema must grant the
    <code class="literal">USAGE</code> privilege on the schema.  To allow users
    to make use of the objects in the schema, additional privileges
    might need to be granted, as appropriate for the object.
   </p><p>
    A user can also be allowed to create objects in someone else's
    schema.  To allow that, the <code class="literal">CREATE</code> privilege on
    the schema needs to be granted.  Note that by default, everyone
    has <code class="literal">CREATE</code> and <code class="literal">USAGE</code> privileges on
    the schema
    <code class="literal">public</code>.  This allows all users that are able to
    connect to a given database to create objects in its
    <code class="literal">public</code> schema.
    Some <a class="link" href="ddl-schemas.html#DDL-SCHEMAS-PATTERNS" title="5.9.6. Usage Patterns">usage patterns</a> call for
    revoking that privilege:
</p><pre class="programlisting">
REVOKE CREATE ON SCHEMA public FROM PUBLIC;
</pre><p>
    (The first <span class="quote">“<span class="quote">public</span>”</span> is the schema, the second
    <span class="quote">“<span class="quote">public</span>”</span> means <span class="quote">“<span class="quote">every user</span>”</span>.  In the
    first sense it is an identifier, in the second sense it is a
    key word, hence the different capitalization; recall the
    guidelines from <a class="xref" href="sql-syntax-lexical.html#SQL-SYNTAX-IDENTIFIERS" title="4.1.1. Identifiers and Key Words">Section 4.1.1</a>.)
   </p></div><div class="sect2" id="DDL-SCHEMAS-CATALOG"><div class="titlepage"><div><div><h3 class="title">5.9.5. The System Catalog Schema</h3></div></div></div><a id="id-1.5.4.11.11.2" class="indexterm"></a><p>
    In addition to <code class="literal">public</code> and user-created schemas, each
    database contains a <code class="literal">pg_catalog</code> schema, which contains
    the system tables and all the built-in data types, functions, and
    operators.  <code class="literal">pg_catalog</code> is always effectively part of
    the search path.  If it is not named explicitly in the path then
    it is implicitly searched <span class="emphasis"><em>before</em></span> searching the path's
    schemas.  This ensures that built-in names will always be
    findable.  However, you can explicitly place
    <code class="literal">pg_catalog</code> at the end of your search path if you
    prefer to have user-defined names override built-in names.
   </p><p>
    Since system table names begin with <code class="literal">pg_</code>, it is best to
    avoid such names to ensure that you won't suffer a conflict if some
    future version defines a system table named the same as your
    table.  (With the default search path, an unqualified reference to
    your table name would then be resolved as the system table instead.)
    System tables will continue to follow the convention of having
    names beginning with <code class="literal">pg_</code>, so that they will not
    conflict with unqualified user-table names so long as users avoid
    the <code class="literal">pg_</code> prefix.
   </p></div><div class="sect2" id="DDL-SCHEMAS-PATTERNS"><div class="titlepage"><div><div><h3 class="title">5.9.6. Usage Patterns</h3></div></div></div><p>
    Schemas can be used to organize your data in many ways.
    A <em class="firstterm">secure schema usage pattern</em> prevents untrusted
    users from changing the behavior of other users' queries.  When a database
    does not use a secure schema usage pattern, users wishing to securely
    query that database would take protective action at the beginning of each
    session.  Specifically, they would begin each session by
    setting <code class="varname">search_path</code> to the empty string or otherwise
    removing non-superuser-writable schemas
    from <code class="varname">search_path</code>.  There are a few usage patterns
    easily supported by the default configuration:
    </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
       Constrain ordinary users to user-private schemas.  To implement this,
       issue <code class="literal">REVOKE CREATE ON SCHEMA public FROM PUBLIC</code>,
       and create a schema for each user with the same name as that user.
       Recall that the default search path starts
       with <code class="literal">$user</code>, which resolves to the user name.
       Therefore, if each user has a separate schema, they access their own
       schemas by default.  After adopting this pattern in a database where
       untrusted users had already logged in, consider auditing the public
       schema for objects named like objects in
       schema <code class="literal">pg_catalog</code>.  This pattern is a secure schema
       usage pattern unless an untrusted user is the database owner or holds
       the <code class="literal">CREATEROLE</code> privilege, in which case no secure
       schema usage pattern exists.
      </p><p>
      </p></li><li class="listitem"><p>
       Remove the public schema from the default search path, by modifying
       <a class="link" href="config-setting.html#CONFIG-SETTING-CONFIGURATION-FILE" title="19.1.2. Parameter Interaction via the Configuration File"><code class="filename">postgresql.conf</code></a>
       or by issuing <code class="literal">ALTER ROLE ALL SET search_path =
       "$user"</code>.  Everyone retains the ability to create objects in
       the public schema, but only qualified names will choose those objects.
       While qualified table references are fine, calls to functions in the
       public schema <a class="link" href="typeconv-func.html" title="10.3. Functions">will be unsafe or
       unreliable</a>.  If you create functions or extensions in the public
       schema, use the first pattern instead.  Otherwise, like the first
       pattern, this is secure unless an untrusted user is the database owner
       or holds the <code class="literal">CREATEROLE</code> privilege.
      </p></li><li class="listitem"><p>
       Keep the default.  All users access the public schema implicitly.  This
       simulates the situation where schemas are not available at all, giving
       a smooth transition from the non-schema-aware world.  However, this is
       never a secure pattern.  It is acceptable only when the database has a
       single user or a few mutually-trusting users.
      </p></li></ul></div><p>
   </p><p>
    For any pattern, to install shared applications (tables to be used by
    everyone, additional functions provided by third parties, etc.), put them
    into separate schemas.  Remember to grant appropriate privileges to allow
    the other users to access them.  Users can then refer to these additional
    objects by qualifying the names with a schema name, or they can put the
    additional schemas into their search path, as they choose.
   </p></div><div class="sect2" id="DDL-SCHEMAS-PORTABILITY"><div class="titlepage"><div><div><h3 class="title">5.9.7. Portability</h3></div></div></div><p>
    In the SQL standard, the notion of objects in the same schema
    being owned by different users does not exist.  Moreover, some
    implementations do not allow you to create schemas that have a
    different name than their owner.  In fact, the concepts of schema
    and user are nearly equivalent in a database system that
    implements only the basic schema support specified in the
    standard.  Therefore, many users consider qualified names to
    really consist of
    <code class="literal"><em class="replaceable"><code>user_name</code></em>.<em class="replaceable"><code>table_name</code></em></code>.
    This is how <span class="productname">PostgreSQL</span> will effectively
    behave if you create a per-user schema for every user.
   </p><p>
    Also, there is no concept of a <code class="literal">public</code> schema in the
    SQL standard.  For maximum conformance to the standard, you should
    not use the <code class="literal">public</code> schema.
   </p><p>
    Of course, some SQL database systems might not implement schemas
    at all, or provide namespace support by allowing (possibly
    limited) cross-database access.  If you need to work with those
    systems, then maximum portability would be achieved by not using
    schemas at all.
   </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ddl-rowsecurity.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ddl.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ddl-inherit.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">5.8. Row Security Policies </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 5.10. Inheritance</td></tr></table></div></body></html>