create_table.sgml

postgresql8.3.4源码,开源数据库

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$PostgreSQL: pgsql/doc/src/sgml/ref/create_table.sgml,v 1.109 2007/07/17 05:02:00 neilc Exp $
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<refentry id="SQL-CREATETABLE">
 <refmeta>
  <refentrytitle id="sql-createtable-title">CREATE TABLE</refentrytitle>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>CREATE TABLE</refname>
  <refpurpose>define a new table</refpurpose>
 </refnamediv>

 <indexterm zone="sql-createtable">
  <primary>CREATE TABLE</primary>
 </indexterm>

 <refsynopsisdiv>
<synopsis>
CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } ] TABLE <replaceable class="PARAMETER">table_name</replaceable> ( [
  { <replaceable class="PARAMETER">column_name</replaceable> <replaceable class="PARAMETER">data_type</replaceable> [ DEFAULT <replaceable>default_expr</> ] [ <replaceable class="PARAMETER">column_constraint</replaceable> [ ... ] ]
    | <replaceable>table_constraint</replaceable>
    | LIKE <replaceable>parent_table</replaceable> [ { INCLUDING | EXCLUDING } { DEFAULTS | CONSTRAINTS | INDEXES } ] ... }
    [, ... ]
] )
[ INHERITS ( <replaceable>parent_table</replaceable> [, ... ] ) ]
[ WITH ( <replaceable class="PARAMETER">storage_parameter</replaceable> [= <replaceable class="PARAMETER">value</replaceable>] [, ... ] ) | WITH OIDS | WITHOUT OIDS ]
[ ON COMMIT { PRESERVE ROWS | DELETE ROWS | DROP } ]
[ TABLESPACE <replaceable class="PARAMETER">tablespace</replaceable> ]

where <replaceable class="PARAMETER">column_constraint</replaceable> is:

[ CONSTRAINT <replaceable class="PARAMETER">constraint_name</replaceable> ]
{ NOT NULL | 
  NULL | 
  UNIQUE <replaceable class="PARAMETER">index_parameters</replaceable> |
  PRIMARY KEY <replaceable class="PARAMETER">index_parameters</replaceable> |
  CHECK ( <replaceable class="PARAMETER">expression</replaceable> ) |
  REFERENCES <replaceable class="PARAMETER">reftable</replaceable> [ ( <replaceable class="PARAMETER">refcolumn</replaceable> ) ] [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ]
    [ ON DELETE <replaceable class="parameter">action</replaceable> ] [ ON UPDATE <replaceable class="parameter">action</replaceable> ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]

and <replaceable class="PARAMETER">table_constraint</replaceable> is:

[ CONSTRAINT <replaceable class="PARAMETER">constraint_name</replaceable> ]
{ UNIQUE ( <replaceable class="PARAMETER">column_name</replaceable> [, ... ] ) <replaceable class="PARAMETER">index_parameters</replaceable> |
  PRIMARY KEY ( <replaceable class="PARAMETER">column_name</replaceable> [, ... ] ) <replaceable class="PARAMETER">index_parameters</replaceable> |
  CHECK ( <replaceable class="PARAMETER">expression</replaceable> ) |
  FOREIGN KEY ( <replaceable class="PARAMETER">column_name</replaceable> [, ... ] ) REFERENCES <replaceable class="PARAMETER">reftable</replaceable> [ ( <replaceable class="PARAMETER">refcolumn</replaceable> [, ... ] ) ]
    [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ] [ ON DELETE <replaceable class="parameter">action</replaceable> ] [ ON UPDATE <replaceable class="parameter">action</replaceable> ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]

<replaceable class="PARAMETER">index_parameters</replaceable> in <literal>UNIQUE</> and <literal>PRIMARY KEY</> constraints are:

[ WITH ( <replaceable class="PARAMETER">storage_parameter</replaceable> [= <replaceable class="PARAMETER">value</replaceable>] [, ... ] ) ]
[ USING INDEX TABLESPACE <replaceable class="PARAMETER">tablespace</replaceable> ]
</synopsis>

 </refsynopsisdiv>

 <refsect1 id="SQL-CREATETABLE-description">
  <title>Description</title>

  <para>
   <command>CREATE TABLE</command> will create a new, initially empty table
   in the current database. The table will be owned by the user issuing the
   command.
  </para>

  <para>
   If a schema name is given (for example, <literal>CREATE TABLE
   myschema.mytable ...</>) then the table is created in the specified
   schema.  Otherwise it is created in the current schema.  Temporary
   tables exist in a special schema, so a schema name cannot be given
   when creating a temporary table.  The name of the table must be
   distinct from the name of any other table, sequence, index, or view
   in the same schema.
  </para>

  <para>
   <command>CREATE TABLE</command> also automatically creates a data
   type that represents the composite type corresponding
   to one row of the table.  Therefore, tables cannot have the same
   name as any existing data type in the same schema.
  </para>

  <para>
   The optional constraint clauses specify constraints (tests) that
   new or updated rows must satisfy for an insert or update operation
   to succeed.  A constraint is an SQL object that helps define the
   set of valid values in the table in various ways.
  </para>

  <para>
   There are two ways to define constraints: table constraints and
   column constraints.  A column constraint is defined as part of a
   column definition.  A table constraint definition is not tied to a
   particular column, and it can encompass more than one column.
   Every column constraint can also be written as a table constraint;
   a column constraint is only a notational convenience for use when the
   constraint only affects one column.
  </para>
 </refsect1>

 <refsect1>
  <title>Parameters</title>

  <variablelist>

   <varlistentry>
    <term><literal>TEMPORARY</> or <literal>TEMP</></term>
    <listitem>
     <para>
      If specified, the table is created as a temporary table.
      Temporary tables are automatically dropped at the end of a
      session, or optionally at the end of the current transaction
      (see <literal>ON COMMIT</literal> below).  Existing permanent
      tables with the same name are not visible to the current session
      while the temporary table exists, unless they are referenced
      with schema-qualified names. Any indexes created on a temporary
      table are automatically temporary as well.
     </para>

     <para>
      Optionally, <literal>GLOBAL</literal> or <literal>LOCAL</literal>
      can be written before <literal>TEMPORARY</> or <literal>TEMP</>.
      This makes no difference in <productname>PostgreSQL</>, but see
      <xref linkend="sql-createtable-compatibility"
      endterm="sql-createtable-compatibility-title">.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="PARAMETER">table_name</replaceable></term>
    <listitem>
     <para>
      The name (optionally schema-qualified) of the table to be created.
     </para>
    </listitem>
   </varlistentry>

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

   <varlistentry>
    <term><replaceable class="PARAMETER">data_type</replaceable></term>
    <listitem>
     <para>
      The data type of the column. This can include array
      specifiers. For more information on the data types supported by
      <productname>PostgreSQL</productname>, refer to <xref
      linkend="datatype">.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>DEFAULT
    <replaceable>default_expr</replaceable></literal></term>
    <listitem>
     <para>
      The <literal>DEFAULT</> clause assigns a default data value for
      the column whose column definition it appears within.  The value
      is any variable-free expression (subqueries and cross-references
      to other columns in the current table are not allowed).  The
      data type of the default expression must match the data type of the
      column.
     </para>

     <para>
      The default expression will be used in any insert operation that
      does not specify a value for the column.  If there is no default
      for a column, then the default is null.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>INHERITS ( <replaceable>parent_table</replaceable> [, ... ] )</literal></term>
    <listitem>
     <para>
      The optional <literal>INHERITS</> clause specifies a list of
      tables from which the new table automatically inherits all
      columns.
     </para>

     <para>
      Use of <literal>INHERITS</> creates a persistent relationship
      between the new child table and its parent table(s).  Schema
      modifications to the parent(s) normally propagate to children
      as well, and by default the data of the child table is included in
      scans of the parent(s).
     </para>

     <para>
      If the same column name exists in more than one parent
      table, an error is reported unless the data types of the columns
      match in each of the parent tables.  If there is no conflict,
      then the duplicate columns are merged to form a single column in
      the new table.  If the column name list of the new table
      contains a column name that is also inherited, the data type must
      likewise match the inherited column(s), and the column
      definitions are merged into one.  However, inherited and new
      column declarations of the same name need not specify identical
      constraints: all constraints provided from any declaration are
      merged together and all are applied to the new table.  If the
      new table explicitly specifies a default value for the column,
      this default overrides any defaults from inherited declarations
      of the column.  Otherwise, any parents that specify default
      values for the column must all specify the same default, or an
      error will be reported.
     </para>
<!--
     <para>
      <productname>PostgreSQL</> automatically allows the
     created table to inherit
      functions on tables above it in the inheritance hierarchy; that
      is, if we create table <literal>foo</literal> inheriting from
      <literal>bar</literal>, then functions that accept the tuple
      type <literal>bar</literal> can also be applied to instances of
      <literal>foo</literal>.  (Currently, this works reliably for
      functions on the first or only parent table, but not so well for
      functions on additional parents.)
     </para>
-->
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>LIKE <replaceable>parent_table</replaceable> [ { INCLUDING | EXCLUDING } { DEFAULTS | CONSTRAINTS | INDEXES } ]</literal></term>
    <listitem>
     <para>
      The <literal>LIKE</literal> clause specifies a table from which
      the new table automatically copies all column names, their data types,
      and their not-null constraints.
     </para>
     <para>
      Unlike <literal>INHERITS</literal>, the new table and original table
      are completely decoupled after creation is complete.  Changes to the
      original table will not be applied to the new table, and it is not
      possible to include data of the new table in scans of the original
      table.
     </para>
     <para>
      Default expressions for the copied column definitions will only be
      copied if <literal>INCLUDING DEFAULTS</literal> is specified.  The
      default behavior is to exclude default expressions, resulting in the
      copied columns in the new table having null defaults.
     </para>
     <para>
      Not-null constraints are always copied to the new table.
      <literal>CHECK</literal> constraints will only be copied if
      <literal>INCLUDING CONSTRAINTS</literal> is specified; other types of
      constraints will never be copied. Also, no distinction is made between
      column constraints and table constraints &mdash; when constraints are
      requested, all check constraints are copied.
     </para>
     <para>
      Any indexes on the original table will not be created on the new
      table, unless the <literal>INCLUDING INDEXES</literal> clause is
      specified.
     </para>
     <para>
      Note also that unlike <literal>INHERITS</literal>, copied columns and
      constraints are not merged with similarly named columns and constraints.
      If the same name is specified explicitly or in another
      <literal>LIKE</literal> clause, an error is signalled.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>CONSTRAINT <replaceable class="PARAMETER">constraint_name</replaceable></literal></term>
    <listitem>
     <para>
      An optional name for a column or table constraint.  If the
      constraint is violated, the constraint name is present in error messages,
      so constraint names like <literal>col must be positive</> can be used
      to communicate helpful constraint information to client applications.
      (Double-quotes are needed to specify constraint names that contain spaces.)
      If a constraint name is not specified, the system generates a name.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>NOT NULL</></term>
    <listitem>
     <para>
      The column is not allowed to contain null values.
     </para>
    </listitem>
   </varlistentry>

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

     <para>
      This clause is only provided for compatibility with
      non-standard SQL databases.  Its use is discouraged in new
      applications.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>UNIQUE</> (column constraint)</term>
    <term><literal>UNIQUE ( <replaceable class="PARAMETER">column_name</replaceable> [, ... ] )</> (table constraint)</term>

    <listitem>
     <para>
      The <literal>UNIQUE</literal> constraint specifies that a
      group of one or more columns of a table can contain
      only unique values. The behavior of the unique table constraint
      is the same as that for column constraints, with the additional
      capability to span multiple columns.
     </para>

     <para>
      For the purpose of a unique constraint, null values are not
      considered equal.
     </para>

     <para>
      Each unique table constraint must name a set of columns that is
      different from the set of columns named by any other unique or
      primary key constraint defined for the table.  (Otherwise it
      would just be the same constraint listed twice.)
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>PRIMARY KEY</> (column constraint)</term>
    <term><literal>PRIMARY KEY ( <replaceable class="PARAMETER">column_name</replaceable> [, ... ] )</> (table constraint)</term>
    <listitem>
     <para>
      The primary key constraint specifies that a column or columns of a table
      can contain only unique (non-duplicate), nonnull values.
      Technically, <literal>PRIMARY KEY</literal> is merely a
      combination of <literal>UNIQUE</> and <literal>NOT NULL</>, but
      identifying a set of columns as primary key also provides
      metadata about the design of the schema, as a primary key
      implies that other tables
      can rely on this set of columns as a unique identifier for rows.
     </para>

     <para>
      Only one primary key can be specified for a table, whether as a