create_table.sgml

关系型数据库 Postgresql 6.5.2

<refentry id="SQL-CREATETABLE">
 <refmeta>
  <refentrytitle>
   CREATE TABLE
  </refentrytitle>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>
 <refnamediv>
  <refname>
   CREATE TABLE
  </refname>
  <refpurpose>
   Creates a new table
  </refpurpose>
 </refnamediv>
 <refsynopsisdiv>
  <refsynopsisdivinfo>
   <date>1998-09-11</date>
  </refsynopsisdivinfo>
  <synopsis>
CREATE [ TEMPORARY | TEMP ] TABLE <replaceable class="PARAMETER">table</replaceable> (
    <replaceable class="PARAMETER">column</replaceable> <replaceable class="PARAMETER">type</replaceable>
    [ NULL | NOT NULL ] [ UNIQUE ] [ DEFAULT <replaceable class="PARAMETER">value</replaceable> ]
    [<replaceable>column_constraint_clause</replaceable> | PRIMARY KEY } [ ... ] ]
    [, ... ]
    [, PRIMARY KEY ( <replaceable class="PARAMETER">column</replaceable> [, ...] ) ]
    [, CHECK ( <replaceable class="PARAMETER">condition</replaceable> ) ]
    [, <replaceable>table_constraint_clause</replaceable> ]
    ) [ INHERITS ( <replaceable>inherited_table</replaceable> [, ...] ) ]
  </synopsis>
  
  <refsect2 id="R2-SQL-CREATETABLE-1">
   <refsect2info>
    <date>1998-09-11</date>
   </refsect2info>
   <title>
    Inputs
   </title>

   <para>

    <variablelist>
     <varlistentry>
      <term>TEMPORARY</term>
      <listitem>
       <para>
	The table is created only for this session, and is
	automatically dropped on session exit.
	Existing permanent tables with the same name are not visible
	while the temporary table exists.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="PARAMETER">table</replaceable></term>
      <listitem>
       <para>
	The name of a new table to be created.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="PARAMETER">column</replaceable></term>
      <listitem>
       <para>
	The name of a column.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="PARAMETER">type</replaceable></term>
      <listitem>
       <para>
	The type of the column. This may include array specifiers.
	Refer to the <citetitle>PostgreSQL User's Guide</citetitle> for
	further information about data types and arrays.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>DEFAULT <replaceable class="PARAMETER">value</replaceable></term>
      <listitem>
       <para>
	A default value for a column.
	See the DEFAULT clause for more information.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable>column_constraint_clause</replaceable></term>
      <listitem>
       <para>
	The optional column constraint clauses specify a list of integrity 
	constraints or tests which new or updated entries must satisfy for
	an insert or update operation to succeed. Each constraint
	must evaluate to a boolean expression. Although <acronym>SQL92</acronym>
	requires the <replaceable class="PARAMETER">column_constraint_clause</replaceable>
	to refer to that column only, <productname>Postgres</productname>
	allows multiple columns
	to be referenced within a single column constraint.
	See the column constraint clause for more information.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable>table_constraint_clause</replaceable></term>
      <listitem>
       <para>
	The optional table CONSTRAINT clause specifies a list of integrity 
	constraints which new or updated entries must satisfy for
	an insert or update operation to succeed. Each constraint
	must evaluate to a boolean expression. Multiple columns
	may be referenced within a single constraint.
	Only one PRIMARY KEY clause may be specified for a table;
	PRIMARY KEY <replaceable>column</replaceable>
	(a table constraint) and PRIMARY KEY (a column constraint) are
	mutually exclusive..
	See the table constraint clause for more information.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>INHERITS <replaceable class="PARAMETER">inherited_table</replaceable></term>
      <listitem>
       <para>
	The optional INHERITS clause specifies a collection of table
	names from which this table automatically inherits all fields.
	If any inherited field name appears more than once, 
	<productname>Postgres</productname>
	reports an error.
	<productname>Postgres</productname> automatically allows the created
	table to inherit functions on tables above it in the inheritance
	hierarchy.
	<note>
	 <title>Aside</title>
	 <para>
	  Inheritance of functions is done according
	  to the conventions of the Common Lisp Object System (CLOS).
	 </para>
	</note>
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>    
  </refsect2>

  <refsect2 id="R2-SQL-CREATETABLE-2">
   <refsect2info>
    <date>1998-09-11</date>
   </refsect2info>
   <title>
    Outputs
   </title>
   <para>

    <variablelist>
     <varlistentry>
      <term><computeroutput>
CREATE
       </computeroutput></term>
      <listitem>
       <para>
	Message returned if table is successfully created.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><computeroutput>
ERROR
       </computeroutput></term>
      <listitem>
       <para>
	Message returned if table creation failed.
	This is usually accompanied by some descriptive text, such as:
	<computeroutput>
ERROR:  Relation '<replaceable class="parameter">table</replaceable>' already exists
	</computeroutput>
	which occurs at runtime, if the table specified already exists
	in the database.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><computeroutput>
ERROR:  DEFAULT: type mismatched
       </computeroutput></term>
      <listitem>
       <para>
	If data type of default value doesn't match the
	column definition's data type.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
  </refsect2>
 </refsynopsisdiv>

 <refsect1 id="R1-SQL-CREATETABLE-1">
  <refsect1info>
   <date>1998-09-11</date>
  </refsect1info>
  <title>
   Description
  </title>
  <para>
   <command>CREATE TABLE</command> will enter a new table into the current data
   base. The table will be "owned" by the user issuing the
   command.
  </para>
  <para>
   The new table is created as a heap with no initial data.
   A table can have no more than 1600 columns (realistically,
   this is limited by the fact that tuple sizes must
   be less than 8192 bytes), but this limit may be configured
   lower at some sites. A table cannot have the same name as
   a system catalog table.
  </para>
 </refsect1>

 <refsect1 id="R1-SQL-DEFAULTCLAUSE-1">
  <refsect1info>
   <date>1998-09-11</date>
  </refsect1info>
  <title>
   DEFAULT Clause
  </title>
  <para>
   <synopsis>
DEFAULT <replaceable class="PARAMETER">value</replaceable>
   </synopsis>
  </para>
  <refsect2 id="R2-SQL-DEFAULTCLAUSE-1">
   <refsect2info>
    <date>1998-09-11</date>
   </refsect2info>
   <title>
    Inputs
   </title>
   <para>

    <variablelist>
     <varlistentry>
      <term><replaceable class="parameter">value</replaceable></term>
      <listitem>
       <para>
	The possible values for the default value expression are:
	<itemizedlist>
	 <listitem>
	  <simpara>
	   a literal value
	  </simpara>
	 </listitem>
	 <listitem>
	  <simpara>
	   a user function
	  </simpara>
	 </listitem>
	 <listitem>
	  <simpara>
	   a niladic function
	  </simpara>
	 </listitem>
	</itemizedlist>
       </para>
      </listitem>
     </varlistentry>	
    </variablelist>
   </para>
  </refsect2>

  <refsect2 id="R2-SQL-DEFAULTCLAUSE-2">
   <refsect2info>
    <date>1998-09-11</date>
   </refsect2info>
   <title>
    Outputs
   </title>
   <para>
    None.
   </para>
  </refsect2>
  
  <refsect2 id="R2-SQL-DEFAULTCLAUSE-3">
   <refsect2info>
    <date>1998-09-11</date>
   </refsect2info>
   <title>
    Description
   </title>
   <para>
    The DEFAULT clause assigns a default data value to a column
    (via a column definition in the CREATE TABLE statement). 
    The data type of a default value must match the column definition's
    data type.
   </para>
   <para>
    An INSERT operation that includes a column without a specified
    default value will assign the NULL value to the column
    if no explicit data value is provided for it.
    Default <replaceable class="parameter">literal</replaceable> means
    that the default is the specified constant value.
    Default <replaceable class="parameter">niladic-function</replaceable>
    or <replaceable class="parameter">user-function</replaceable> means
    that the default
    is the value of the specified function at the time of the INSERT.
   </para>
   <para>
    There are two types of niladic functions:
    <variablelist>
     <varlistentry>
      <term>niladic USER</term>
      <listitem>
       <variablelist>
	<varlistentry>
	 <term>CURRENT_USER / USER</term>
	 <listitem>
	  <simpara>See CURRENT_USER function</simpara>
	 </listitem>
	</varlistentry>
	<varlistentry>
	 <term>SESSION_USER</term>
	 <listitem>
	  <simpara>not yet supported</simpara>
	 </listitem>
	</varlistentry>
	<varlistentry>
	 <term>SYSTEM_USER</term>
	 <listitem>
	  <simpara>not yet supported</simpara>
	 </listitem>
	</varlistentry>
       </variablelist>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term>niladic datetime</term>
      <listitem>
       <variablelist>
	<varlistentry>
	 <term>CURRENT_DATE</term>
	 <listitem>
	  <simpara>See CURRENT_DATE function</simpara>
	 </listitem>
	</varlistentry>
	<varlistentry>
	 <term>CURRENT_TIME</term>
	 <listitem>
	  <simpara>See CURRENT_TIME function</simpara>
	 </listitem>
	</varlistentry>
	<varlistentry>
	 <term>CURRENT_TIMESTAMP</term>
	 <listitem>
	  <simpara>See CURRENT_TIMESTAMP function</simpara>
	 </listitem>
	</varlistentry>
       </variablelist>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>

   <para>
    In the current release (v6.5), <productname>Postgres</productname>
    evaluates all default expressions at the time the table is defined.
    Hence, functions which are "non-cacheable" such as
    <function>CURRENT_TIMESTAMP</function> may not produce the desired
    effect. For the particular case of date/time types, one can work
    around this behavior by using 
    <quote>DEFAULT TEXT 'now'</quote>
    instead of
    <quote>DEFAULT 'now'</quote>
    or
    <quote>DEFAULT CURRENT_TIMESTAMP</quote>.
    This forces <productname>Postgres</productname> to consider the constant a string
    type and then to convert the value to <type>timestamp</type> at runtime.
   </para>
  </refsect2>
  <refsect2 id="R2-SQL-DEFAULTCLAUSE-4">
   <refsect2info>
    <date>1998-09-11</date>
   </refsect2info>
   <title>
    Usage
   </title>

   <para>
    To assign a constant value as the default for the
    columns <literal>did</literal> and <literal>number</literal>,
    and a string literal to the column <literal>did</literal>:

    <programlisting>
CREATE TABLE video_sales (
    did      VARCHAR(40) DEFAULT 'luso films',
    number   INTEGER DEFAULT 0,
    total    CASH DEFAULT '$0.0'
);
    </programlisting>
   </para>
   <para>
    To assign an existing sequence
    as the default for the column <literal>did</literal>,
    and a literal to the column <literal>name</literal>:

    <programlisting>
CREATE TABLE distributors (
    did      DECIMAL(3)  DEFAULT NEXTVAL('serial'),
    name     VARCHAR(40) DEFAULT 'luso films'
);
    </programlisting>
   </para>
  </refsect2>
 </refsect1>

 <refsect1 id="R1-SQL-COLUMNCONSTRAINT-1">
  <refsect1info>
   <date>1998-09-11</date>
  </refsect1info>
  <title>
   Column CONSTRAINT Clause
  </title>
  <para>
   <synopsis>
[ CONSTRAINT <replaceable class="parameter">name</replaceable> ] { [
    NULL | NOT NULL ] | UNIQUE | PRIMARY KEY | CHECK <replaceable
     class="parameter">constraint</replaceable> } [, ...]
   </synopsis>
  </para>

  <refsect2 id="R2-SQL-COLUMNCONSTRAINT-1">
   <refsect2info>
    <date>1998-09-11</date>
   </refsect2info>
   <title>
    Inputs
   </title>
   <para>
    <variablelist>
     <varlistentry>
      <term><replaceable class="parameter">name</replaceable></term>
      <listitem>
       <para>
	An arbitrary name given to the integrity constraint. 
	If <replaceable class="parameter">name</replaceable> is not specified,
	it is generated from the table and column names,
	which should ensure uniqueness for
	<replaceable class="parameter">name</replaceable>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>NULL</term>
      <listitem>
       <para>
	The column is allowed to contain NULL values. This is the default.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>NOT NULL</term>
      <listitem>
       <para>
	The column is not allowed to contain NULL values.
	This is equivalent to the column constraint
	CHECK (<replaceable class="PARAMETER">column</replaceable> NOT NULL).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>UNIQUE</term>
      <listitem>
       <para>
	The column must have unique values. In <productname>Postgres</productname>
	this is enforced by an implicit creation of a unique index on the table.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>PRIMARY KEY</term>
      <listitem>
       <para>
	This column is a primary key, which implies that uniqueness is
	enforced by the system and that other tables may rely on this column
	as a unique identifier for rows.
	See PRIMARY KEY for more information.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>
<replaceable class="parameter">constraint</replaceable>
      </term>
      <listitem>
       <para>
	The definition of the constraint.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
  </refsect2>

  <refsect2 id="R2-SQL-COLUMNCONSTRAINT-2">
   <refsect2info>
    <date>1998-09-11</date>
   </refsect2info>
   <title>
    Description
   </title>
   <para>
    A Constraint is a named rule: an SQL object which helps define
    valid sets of values by putting limits on the results of INSERT,
    UPDATE or DELETE operations performed on a Base Table. 
   </para>
   <para>
    There are two ways to define integrity constraints:
    table constraints, covered later, and column constraints, covered here.
   </para>
   <para>
    A column constraint is an integrity constraint defined as part
    of a column definition, and logically becomes a table
    constraint as soon as it is created. The column
    constraints available are:
    <simplelist columns="1">
     <member>PRIMARY KEY</member>
     <member>REFERENCES</member>
     <member>UNIQUE</member>
     <member>CHECK</member>
     <member>NOT NULL</member>
    </simplelist></para>
   <note>
    <para>
     <productname>Postgres</productname> does not yet 
     (at release 6.5) support
     REFERENCES integrity constraints. The parser
     accepts the REFERENCES syntax but ignores the clause.
    </para>
   </note>
  </refsect2>
   
  <refsect2 id="R2-SQL-NOTNULL-1">
   <refsect2info>
    <date>1998-09-11</date>
   </refsect2info>
   <title>
    NOT NULL Constraint
   </title>
   <synopsis>
[ CONSTRAINT <replaceable class="parameter">name</replaceable> ] NOT NULL 
   </synopsis>
   <para>