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Commitbac3e83

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Replace the hard-wired type knowledge in TypeCategory() and IsPreferredType()
with system catalog lookups, as was foreseen to be necessary almost sincetheir creation. Instead put the information into two new pg_type columns,typcategory and typispreferred. Add support for setting these whencreating a user-defined base type.The category column is just a "char" (i.e. a poor man's enum), allowinga crude form of user extensibility of the category list: just use anotherwise-unused character. This seems sufficient for foreseen uses,but we could upgrade to having an actual category catalog someday, ifthere proves to be a huge demand for custom type categories.In this patch I have attempted to hew exactly to the behavior of theprevious hardwired logic, except for introducing new type categories forarrays, composites, and enums. In particular the default preferred statefor user-defined types remains TRUE. That seems worth revisiting, but itshould be done as a separate patch from introducing the infrastructure.Likewise, any adjustment of the standard set of categories should be doneseparately.
1 parentab9907f commitbac3e83

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20 files changed

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20 files changed

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‎doc/src/sgml/catalogs.sgml

Lines changed: 114 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -1,4 +1,4 @@
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<!-- $PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.171 2008/07/18 03:32:51 tgl Exp $ -->
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<!-- $PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.172 2008/07/30 17:05:04 tgl Exp $ -->
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<!--
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Documentation of the system catalogs, directed toward PostgreSQL developers
44
-->
@@ -994,7 +994,7 @@
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<entry><type>int4</type></entry>
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<entry></entry>
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<entry>
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The number of direct ancestors this column has. A column with a
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The number of direct ancestors this column has. A column with a
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nonzero number of ancestors cannot be dropped nor renamed
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</entry>
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</row>
@@ -1005,7 +1005,7 @@
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<para>
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In a dropped column's <structname>pg_attribute</structname> entry,
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<structfield>atttypid</structfield> is reset to zero, but
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<structfield>atttypid</structfield> is reset to zero, but
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<structfield>attlen</structfield> and the other fields copied from
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<structname>pg_type</> are still valid. This arrangement is needed
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to cope with the situation where the dropped column's data type was
@@ -1118,7 +1118,7 @@
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<entry><structfield>rolconnlimit</structfield></entry>
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<entry><type>int4</type></entry>
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<entry>
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For roles that can log in, this sets maximum number of concurrent
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For roles that can log in, this sets maximum number of concurrent
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connections this role can make. -1 means no limit
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</entry>
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</row>
@@ -2169,7 +2169,7 @@
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<entry><type>int4</type></entry>
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<entry></entry>
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<entry>
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Sets maximum number of concurrent connections that can be made
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Sets maximum number of concurrent connections that can be made
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to this database. -1 means no limit
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</entry>
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</row>
@@ -4855,7 +4855,7 @@
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<para>
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The catalog <structname>pg_type</structname> stores information about data
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types. Base types (scalar types) are created with
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types. Base typesand enum types(scalar types) are created with
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<xref linkend="sql-createtype" endterm="sql-createtype-title">, and
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domains with
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<xref linkend="sql-createdomain" endterm="sql-createdomain-title">.
@@ -4926,8 +4926,7 @@
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where Datum is 8 bytes).
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Variable-length types are always passed by reference. Note that
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<structfield>typbyval</structfield> can be false even if the
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length would allow pass-by-value; this is currently true for
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type <type>float4</type>, for example
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length would allow pass-by-value
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</entry>
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</row>
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@@ -4947,6 +4946,28 @@
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</entry>
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</row>
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<row>
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<entry><structfield>typcategory</structfield></entry>
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<entry><type>char</type></entry>
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<entry></entry>
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<entry>
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<structfield>typcategory</structfield> is an arbitrary classification
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of data types that is used by the parser to determine which implicit
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casts should be <quote>preferred</>.
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See <xref linkend="catalog-typcategory-table">
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</entry>
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</row>
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<row>
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<entry><structfield>typispreferred</structfield></entry>
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<entry><type>bool</type></entry>
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<entry></entry>
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<entry>
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True if the type is a preferred cast target within its
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<structfield>typcategory</structfield>
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</entry>
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</row>
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<row>
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<entry><structfield>typisdefined</structfield></entry>
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<entry><type>bool</type></entry>
@@ -5217,6 +5238,86 @@
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</tbody>
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</tgroup>
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</table>
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<para>
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<xref linkend="catalog-typcategory-table"> lists the system-defined values
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of <structfield>typcategory</>. Any future additions to this list will
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also be upper-case ASCII letters. All other ASCII characters are reserved
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for user-defined categories.
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</para>
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<table id="catalog-typcategory-table">
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<title><structfield>typcategory</> Codes</title>
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<tgroup cols=2>
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<thead>
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<row>
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<entry>Code</entry>
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<entry>Category</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry><literal>A</literal></entry>
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<entry>Array types</entry>
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</row>
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<row>
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<entry><literal>B</literal></entry>
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<entry>Boolean types</entry>
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</row>
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<row>
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<entry><literal>C</literal></entry>
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<entry>Composite types</entry>
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</row>
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<row>
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<entry><literal>D</literal></entry>
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<entry>Date/time types</entry>
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</row>
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<row>
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<entry><literal>E</literal></entry>
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<entry>Enum types</entry>
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</row>
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<row>
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<entry><literal>G</literal></entry>
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<entry>Geometric types</entry>
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</row>
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<row>
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<entry><literal>I</literal></entry>
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<entry>Network address types</entry>
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</row>
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<row>
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<entry><literal>N</literal></entry>
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<entry>Numeric types</entry>
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</row>
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<row>
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<entry><literal>P</literal></entry>
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<entry>Pseudo-types</entry>
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</row>
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<row>
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<entry><literal>S</literal></entry>
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<entry>String types</entry>
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</row>
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<row>
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<entry><literal>T</literal></entry>
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<entry>Timespan types</entry>
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</row>
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<row>
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<entry><literal>U</literal></entry>
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<entry>User-defined types</entry>
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</row>
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<row>
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<entry><literal>V</literal></entry>
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<entry>Bit-string types</entry>
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</row>
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<row>
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<entry><literal>X</literal></entry>
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<entry><type>unknown</> type</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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52205321
</sect1>
52215322

52225323
<sect1 id="views-overview">
@@ -5787,7 +5888,7 @@
57875888
for another transaction, it does so by attempting to acquire share lock on
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the other transaction ID (either virtual or permanent ID depending on the
57895890
situation). That will succeed only when the other transaction
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terminates and releases its locks.
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terminates and releases its locks.
57915892
</para>
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<para>
@@ -6036,7 +6137,7 @@
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<para>
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The view <structname>pg_roles</structname> provides access to
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information about database roles. This is simply a publicly
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readable view of
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readable view of
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<link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>
60416142
that blanks out the password field.
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</para>
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<entry><type>int4</type></entry>
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<entry></entry>
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<entry>
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For roles that can log in, this sets maximum number of concurrent
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For roles that can log in, this sets maximum number of concurrent
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connections this role can make. -1 means no limit
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</entry>
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</row>
@@ -6316,7 +6417,7 @@
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</tbody>
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</tgroup>
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</table>
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<para>
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The <structname>pg_settings</structname> view cannot be inserted into or
63226423
deleted from, but it can be updated. An <command>UPDATE</command> applied
@@ -6774,7 +6875,7 @@
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<para>
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The view <structname>pg_user</structname> provides access to
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information about database users. This is simply a publicly
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readable view of
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readable view of
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<link linkend="view-pg-shadow"><structname>pg_shadow</structname></link>
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that blanks out the password field.
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</para>

‎doc/src/sgml/ref/create_type.sgml

Lines changed: 49 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1,5 +1,5 @@
11
<!--
2-
$PostgreSQL: pgsql/doc/src/sgml/ref/create_type.sgml,v 1.74 2008/05/27 18:05:13 tgl Exp $
2+
$PostgreSQL: pgsql/doc/src/sgml/ref/create_type.sgml,v 1.75 2008/07/30 17:05:04 tgl Exp $
33
PostgreSQL documentation
44
-->
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@@ -38,6 +38,8 @@ CREATE TYPE <replaceable class="parameter">name</replaceable> (
3838
[ , PASSEDBYVALUE ]
3939
[ , ALIGNMENT = <replaceable class="parameter">alignment</replaceable> ]
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[ , STORAGE = <replaceable class="parameter">storage</replaceable> ]
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[ , CATEGORY = <replaceable class="parameter">category</replaceable> ]
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[ , PREFERRED = <replaceable class="parameter">preferred</replaceable> ]
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[ , DEFAULT = <replaceable class="parameter">default</replaceable> ]
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[ , ELEMENT = <replaceable class="parameter">element</replaceable> ]
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[ , DELIMITER = <replaceable class="parameter">delimiter</replaceable> ]
@@ -281,6 +283,27 @@ CREATE TYPE <replaceable class="parameter">name</replaceable>
281283
<literal>external</literal> items.)
282284
</para>
283285

286+
<para>
287+
The <replaceable class="parameter">category</replaceable> and
288+
<replaceable class="parameter">preferred</replaceable> parameters can be
289+
used to help control which implicit cast will be applied in ambiguous
290+
situations. Each data type belongs to a category named by a single ASCII
291+
character, and each type is either <quote>preferred</> or not within its
292+
category. The parser will prefer casting to preferred types (but only from
293+
other types within the same category) when this rule is helpful in
294+
resolving overloaded functions or operators. For more details see <xref
295+
linkend="typeconv">. For types that have no implicit casts to or from any
296+
other types, it is sufficient to leave these settings at the defaults.
297+
However, for a group of related types that have implicit casts, it is often
298+
helpful to mark them all as belonging to a category and select one or two
299+
of the <quote>most general</> types as being preferred within the category.
300+
The <replaceable class="parameter">category</replaceable> parameter is
301+
especially useful when adding a user-defined type to an existing built-in
302+
category, such as the numeric or string types. However, it is also
303+
possible to create new entirely-user-defined type categories. Select any
304+
ASCII character other than an upper-case letter to name such a category.
305+
</para>
306+
284307
<para>
285308
A default value can be specified, in case a user wants columns of the
286309
data type to default to something other than the null value.
@@ -494,6 +517,31 @@ CREATE TYPE <replaceable class="parameter">name</replaceable>
494517
</listitem>
495518
</varlistentry>
496519

520+
<varlistentry>
521+
<term><replaceable class="parameter">category</replaceable></term>
522+
<listitem>
523+
<para>
524+
The category code (a single ASCII character) for this type.
525+
The default is <literal>'U'</> for <quote>user-defined type</>.
526+
Other standard category codes can be found in
527+
<xref linkend="catalog-typcategory-table">. You may also choose
528+
other ASCII characters in order to create custom categories.
529+
</para>
530+
</listitem>
531+
</varlistentry>
532+
533+
<varlistentry>
534+
<term><replaceable class="parameter">preferred</replaceable></term>
535+
<listitem>
536+
<para>
537+
True if this type is a preferred type within its type category,
538+
else false. The default is true (which is appropriate for
539+
all entries in category <literal>U</>, but is usually not
540+
appropriate for new types in other categories &mdash; beware!).
541+
</para>
542+
</listitem>
543+
</varlistentry>
544+
497545
<varlistentry>
498546
<term><replaceable class="parameter">default</replaceable></term>
499547
<listitem>

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