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https://git.postgresql.org/git/postgresql.git
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Start adding some more documentation about the number types. Make
bigserial and alias for serial8 for consistency with bigint/int8.
This commit is contained in:
Peter Eisentraut
parent
e8cb935921
commit
9cf701f324
@ -1,5 +1,5 @@
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<!--
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$Header: /cvsroot/pgsql/doc/src/sgml/datatype.sgml,v 1.58 2001/08/16 20:38:53 tgl Exp $
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$Header: /cvsroot/pgsql/doc/src/sgml/datatype.sgml,v 1.59 2001/08/24 20:03:41 petere Exp $
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-->
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<chapter id="datatype">
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@ -53,6 +53,12 @@ $Header: /cvsroot/pgsql/doc/src/sgml/datatype.sgml,v 1.58 2001/08/16 20:38:53 tg
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<entry>signed eight-byte integer</entry>
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</row>
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<row>
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<entry><type>bigserial</type></entry>
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<entry><type>serial8</type></entry>
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<entry>autoincrementing eight-byte integer</entry>
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</row>
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<row>
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<entry><type>bit</type></entry>
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<entry></entry>
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@ -203,12 +209,6 @@ $Header: /cvsroot/pgsql/doc/src/sgml/datatype.sgml,v 1.58 2001/08/16 20:38:53 tg
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<entry>autoincrementing four-byte integer</entry>
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</row>
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<row>
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<entry><type>serial8</type></entry>
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<entry></entry>
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<entry>autoincrementing eight-byte integer</entry>
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</row>
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<row>
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<entry><type>text</type></entry>
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<entry></entry>
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@ -346,8 +346,8 @@ $Header: /cvsroot/pgsql/doc/src/sgml/datatype.sgml,v 1.58 2001/08/16 20:38:53 tg
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<tgroup cols="4">
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<thead>
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<row>
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<entry>Type Name</entry>
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<entry>Storage</entry>
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<entry>Type name</entry>
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<entry>Storage size</entry>
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<entry>Description</entry>
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<entry>Range</entry>
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</row>
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@ -370,46 +370,46 @@ $Header: /cvsroot/pgsql/doc/src/sgml/datatype.sgml,v 1.58 2001/08/16 20:38:53 tg
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<entry>bigint</entry>
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<entry>8 bytes</entry>
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<entry>Very large range fixed-precision</entry>
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<entry>about 18 decimal places</entry>
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<entry>about 18 decimal digits</entry>
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</row>
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<row>
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<entry>decimal</entry>
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<entry>variable</entry>
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<entry>User-specified precision</entry>
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<entry>user-specified precision, exact</entry>
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<entry>no limit</entry>
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</row>
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<row>
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<entry>numeric</entry>
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<entry>variable</entry>
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<entry>User-specified precision</entry>
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<entry>user-specified precision, exact</entry>
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<entry>no limit</entry>
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</row>
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<row>
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<entry>real</entry>
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<entry>4 bytes</entry>
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<entry>Variable-precision</entry>
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<entry>6 decimal places</entry>
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<entry>variable-precision, inexact</entry>
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<entry>6 decimal digits precision</entry>
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</row>
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<row>
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<entry>double precision</entry>
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<entry>8 bytes</entry>
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<entry>Variable-precision</entry>
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<entry>15 decimal places</entry>
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<entry>variable-precision, inexact</entry>
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<entry>15 decimal digits precision</entry>
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</row>
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<row>
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<entry>serial4</entry>
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<entry>serial</entry>
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<entry>4 bytes</entry>
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<entry>Identifier or cross-reference</entry>
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<entry>autoincrementing integer</entry>
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<entry>1 to 2147483647</entry>
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</row>
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<row>
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<entry>serial8</entry>
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<entry>bigserial</entry>
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<entry>8 bytes</entry>
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<entry>Identifier or cross-reference</entry>
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<entry>autoincrementing integer</entry>
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<entry>1 to 9223372036854775807</entry>
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</row>
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</tbody>
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@ -422,16 +422,188 @@ $Header: /cvsroot/pgsql/doc/src/sgml/datatype.sgml,v 1.58 2001/08/16 20:38:53 tg
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<xref linkend="sql-syntax-constants">. The numeric types have a
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full set of corresponding arithmetic operators and
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functions. Refer to <xref linkend="functions"> for more
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information.
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information. The following sections describe the types in detail.
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</para>
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<sect2 id="datatype-int">
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<title>The Integer Types</title>
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<para>
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The types <type>smallint</type>, <type>integer</type>,
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<type>bigint</type> store whole numbers, that is, numbers without
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fractional components, of various ranges. Attempts to store
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values outside of the allowed range will result in an error.
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</para>
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<para>
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The <type>bigint</type> type may not function correctly on all platforms,
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since it relies on compiler support for eight-byte integers. On a machine
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without such support, <type>bigint</type> acts the same
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as <type>integer</type> (but still takes up eight bytes of storage).
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The type <type>integer</type> is the usual choice, as it offers
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the best balance between range, storage size, and performance.
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The <type>smallint</type> type is generally only used if disk
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space is at a premium. The <type>bigint</type> type should only
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be used if the <type>integer</type> range is not sufficient,
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because the latter is definitely faster.
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</para>
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<para>
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The <type>bigint</type> type may not function correctly on all
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platforms, since it relies on compiler support for eight-byte
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integers. On a machine without such support, <type>bigint</type>
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acts the same as <type>integer</type> (but still takes up eight
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bytes of storage). However, we are not aware of any reasonable
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platform where this is actually the case.
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</para>
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<note>
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<para>
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If you have a column of type <type>smallint</type> or
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<type>bigint</type> with an index, you may encounter problems
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getting the system to use that index. For instance, a clause of
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the form
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<programlisting>
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... WHERE smallint_column = 42
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</programlisting>
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will not use an index, because the system assigns type
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<type>integer</type> to the 42, and PostgreSQL currently cannot
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use an index when two different data types are involved. A
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workaround is to single-quote the constant, thus:
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<programlisting>
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... WHERE smallint_column = '42'
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</programlisting>
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This will cause the system to delay the type resolution and will
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assign the right type to the constant.
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</para>
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</note>
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<para>
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SQL only specifies the integer types <type>integer</type> (or
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<type>int</type>) and <type>smallint</type>. The type
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<type>bigint</type>, and the type names <type>int2</type>,
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<type>int4</type>, and <type>int8</type> are extensions, which
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are shared with various other RDBMS products.
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</para>
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</sect2>
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<sect2 id="datatype-numeric-decimal">
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<title>Arbitrary Precision Numbers</title>
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<para>
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The type <type>numeric</type> can store numbers of practically
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unlimited size and precision, while being able to store all
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numbers and carry out all calculations exactly. It is especially
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recommended for storing monetary amounts and other quantities
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where exactness is required. However, the <type>numeric</type>
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type is very slow compared to the floating point types described
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in the next section.
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</para>
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<para>
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In what follows we use these terms: The
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<firstterm>scale</firstterm> of a <type>numeric</type> is the
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count of decimal digits in the fractional part, to the right of
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the decimal point. The <firstterm>precision</firstterm> of a
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<type>numeric</type> is the total count of significant digits in
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the whole number, that is, the number of digits to both sides of
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the decimal point. So the number 23.5141 has a precision of 6
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and a scale of 4. Integers can be considered to have a scale of
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zero.
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</para>
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<para>
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Both the precision and the scale of the numeric type can be
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configured. To declare a column of type <type>numeric</type> use
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the syntax
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<programlisting>
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NUMERIC(<replaceable>precision</replaceable>, <replaceable>scale</replaceable>)
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</programlisting>
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The precision must be positive, the scale zero or positive.
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Alternatively,
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<programlisting>
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NUMERIC(<replaceable>precision</replaceable>)
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</programlisting>
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selects a scale of 0. Merely specifying
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<programlisting>
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NUMERIC
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</programlisting>
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uses a default precision and scale, which is currently (30,6).
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(The SQL standard requires a default scale of 0. We find this a
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bit useless. If you're concerned about portability, always
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specify the precision and scale explicitly.)
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</para>
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<para>
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If the precision or scale of a value is greater than the declared
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precision or scale of a column, the system will attempt to round
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the value. If the value cannot be rounded so as to satisfy the
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declared limits, an error is raised.
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</para>
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<para>
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The types <type>decimal</type> and <type>numeric</type> are
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equivalent. Both types are part of the SQL standard.
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</para>
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</sect2>
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<sect2 id="datatype-float">
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<title>Floating Point Types</title>
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<para>
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The data types <type>real</type> and <type>double
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precision</type> are inexact, variable precision numeric types.
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In practice, these types are usually implementations of IEEE 754
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binary floating point (single and double precision,
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respectively), to the extent that the underlying processor,
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operating system, and compiler support it.
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</para>
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<para>
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Inexact means that some values cannot be converted exactly to the
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internal format and are stored as approximations, so that storing
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and printing back out a value may show slight discrepancies.
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Managing these errors and how they propagate through calculations
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is the subject of an entire branch of mathematics and computer
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science and will not be discussed further here, except for the
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following points:
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<itemizedlist>
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<listitem>
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<para>
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If you require exact storage and calculations (such as for
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monetary amounts), use the <type>numeric</type> type instead.
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</para>
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</listitem>
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<listitem>
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<para>
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If you want to do complicated calculations with these types
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for anything important, especially if you rely on certain
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behavior in boundary cases (infinity, underflow), you should
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evaluate the implementation carefully.
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</para>
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</listitem>
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<listitem>
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<para>
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Comparing two floating point values for equality may or may
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not work as expected.
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</para>
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</listitem>
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</itemizedlist>
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</para>
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<para>
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Normally, the <type>real</type> type has a range of at least
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-1E+37 to +1E+37 with a precision of at least 6. The
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<type>double precision</type> type normally has a range of around
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-1E+308 to +1E+308 with a precision of at least 15. Values that
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are too large or too small will cause an error. Rounding may
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take place if the precision of an input number is too high.
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Numbers too close to zero that are not representable as distinct
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from zero will cause an underflow error.
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</para>
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</sect2>
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<sect2 id="datatype-serial">
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<title>The Serial Types</title>
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@ -463,17 +635,17 @@ $Header: /cvsroot/pgsql/doc/src/sgml/datatype.sgml,v 1.58 2001/08/16 20:38:53 tg
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in tables.
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In the current implementation, specifying
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<programlisting>
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<programlisting>
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CREATE TABLE <replaceable class="parameter">tablename</replaceable> (<replaceable class="parameter">colname</replaceable> SERIAL);
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</programlisting>
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</programlisting>
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is equivalent to specifying:
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<programlisting>
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<programlisting>
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CREATE SEQUENCE <replaceable class="parameter">tablename</replaceable>_<replaceable class="parameter">colname</replaceable>_seq;
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CREATE TABLE <replaceable class="parameter">tablename</replaceable>
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(<replaceable class="parameter">colname</replaceable> integer DEFAULT nextval('<replaceable class="parameter">tablename</replaceable>_<replaceable class="parameter">colname</replaceable>_seq') UNIQUE NOT NULL;
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</programlisting>
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(<replaceable class="parameter">colname</replaceable> integer DEFAULT nextval('<replaceable class="parameter">tablename</replaceable>_<replaceable class="parameter">colname</replaceable>_seq') UNIQUE NOT NULL);
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</programlisting>
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Thus, we have created an integer column and arranged for its default
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values to be assigned from a sequence generator. UNIQUE and NOT NULL
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@ -492,10 +664,10 @@ CREATE TABLE <replaceable class="parameter">tablename</replaceable>
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<para>
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The type names <type>serial</type> and <type>serial4</type> are
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equivalent: both create <type>integer</type> columns. The type
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name <type>serial8</type> works just the same way, except that it
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creates a <type>bigint</type> column. <type>serial8</type> should
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be used if you anticipate use of more than 2^31 identifiers over
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the lifetime of the table.
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names <type>bigserial</type> and <type>serial8</type> works just
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the same way, except that it creates a <type>bigint</type>
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column. <type>serial8</type> should be used if you anticipate
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use of more than 2^31 identifiers over the lifetime of the table.
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</para>
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<para>
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@ -503,11 +675,11 @@ CREATE TABLE <replaceable class="parameter">tablename</replaceable>
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not automatically dropped when a table containing a serial type
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is dropped. So, the following commands executed in order will likely fail:
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<programlisting>
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<programlisting>
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CREATE TABLE <replaceable class="parameter">tablename</replaceable> (<replaceable class="parameter">colname</replaceable> SERIAL);
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DROP TABLE <replaceable class="parameter">tablename</replaceable>;
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CREATE TABLE <replaceable class="parameter">tablename</replaceable> (<replaceable class="parameter">colname</replaceable> SERIAL);
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</programlisting>
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</programlisting>
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The sequence will remain in the database until explicitly dropped using
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<command>DROP SEQUENCE</command>.
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@ -6,7 +6,7 @@
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* Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $Header: /cvsroot/pgsql/src/backend/parser/analyze.c,v 1.196 2001/08/21 16:36:03 tgl Exp $
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* $Header: /cvsroot/pgsql/src/backend/parser/analyze.c,v 1.197 2001/08/24 20:03:45 petere Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -732,7 +732,8 @@ transformCreateStmt(ParseState *pstate, CreateStmt *stmt)
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is_serial = true;
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column->typename->name = pstrdup("int4");
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}
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else if (strcmp(column->typename->name, "serial8") == 0)
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else if (strcmp(column->typename->name, "bigserial") == 0 ||
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strcmp(column->typename->name, "serial8") == 0)
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{
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is_serial = true;
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column->typename->name = pstrdup("int8");
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