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TITLE="PostgreSQL 9.1beta1 Documentation"
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HREF="index.html"><LINK
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TITLE="System Catalogs"
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HREF="catalogs.html"><LINK
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TITLE="pg_auth_members"
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CONTENT="2011-04-27T21:20:33"></HEAD
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SUMMARY="Header navigation table"
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>PostgreSQL 9.1beta1 Documentation</A
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TITLE="pg_auth_members"
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HREF="catalog-pg-auth-members.html"
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TITLE="System Catalogs"
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>Chapter 45. System Catalogs</TD
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TITLE="System Catalogs"
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HREF="catalog-pg-class.html"
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NAME="CATALOG-PG-CAST"
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> stores data type conversion
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paths, both built-in paths and those defined with
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HREF="sql-createcast.html"
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> It should be noted that <TT
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every type conversion that the system knows how to perform; only those that
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cannot be deduced from some generic rule. For example, casting between a
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domain and its base type is not explicitly represented in
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>. Another important exception is that
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>"automatic I/O conversion casts"</SPAN
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>, those performed using a data
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type's own I/O functions to convert to or from <TT
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string types, are not explicitly represented in
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><COL><COL><COL><COL><THEAD
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HREF="catalog-pg-type.html"
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>OID of the source data type</TD
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HREF="catalog-pg-type.html"
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>OID of the target data type</TD
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HREF="catalog-pg-proc.html"
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> The OID of the function to use to perform this cast. Zero is
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stored if the cast method doesn't require a function.
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> Indicates what contexts the cast can be invoked in.
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> means only as an explicit cast (using
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> means implicitly in assignment
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to a target column, as well as explicitly.
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> means implicitly in expressions, as well as the
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> Indicates how the cast is performed.
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> means that the function specified in the <TT
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> means that the input/output functions are used.
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> means that the types are binary-coercible, thus no conversion is required.
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> The cast functions listed in <TT
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always take the cast source type as their first argument type, and
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return the cast destination type as their result type. A cast
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function can have up to three arguments. The second argument,
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if present, must be type <TT
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>; it receives the type
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modifier associated with the destination type, or -1
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if there is none. The third argument,
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if present, must be type <TT
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if the cast is an explicit cast, <TT
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> It is legitimate to create a <TT
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in which the source and target types are the same, if the associated
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function takes more than one argument. Such entries represent
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>"length coercion functions"</SPAN
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> that coerce values of the type
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to be legal for a particular type modifier value.
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> entry has different source and
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target types and a function that takes more than one argument, it
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represents converting from one type to another and applying a length
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coercion in a single step. When no such entry is available, coercion
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to a type that uses a type modifier involves two steps, one to
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convert between data types and a second to apply the modifier.
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HREF="catalog-pg-class.html"
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