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CREATE CAST��Ѥ��ȡ��㥹�Ȥ��Ǥ��ޤ�� 㥹�Ȥˤ�ꡢ2�ĤΥǡ��֤��Ѵ��ˡ��ꤷ�ޤ�� ʲ��򼨤��ޤ��

SELECT CAST(42 AS text);

��ν��¹Ԥ��ȡ��˻��ꤵ�줿�ؿ��ξ��text(int4)��ƤӽФ��42��text�ǡ��Ѵ��ޤ�� (Ŭ�ڤʥ��㥹�Ȥ��Ƥ��ʤ��硢�Ѵ��ϼ��Ԥ��ޤ��)

2�ĤΥǡ��ϡ��Х��ʥ�ߴ����礬��ޤ�� Ĥޤꡢ"��ͳ��"�ؿ��ƤӽФ��Ȥʤ��ߤ��Υǡ��Ѵ��뤳�Ȥ��Ǥ��ޤ�� ξ�硢�б��ͤϡ�Ʊ��ɽ��Ѥ��Ƥ��ɬ�פ��ޤ�� 㤨�С��ǡ��text��varchar�ϡ��Х��ʥ�ߴ��ޤ��

�ǥե��ȤǤϡ��㥹�Ȥ��Ū�ʥ��㥹��׵᤬��ä��Τ߸ƤӽФ��ǽ�Ǥ�� Ū�ʥ��㥹�Ȥι�ʸ�Ȥϡ�CAST(x AS typename)��⤷��ϡ�x::typename�Ǥ��

��㥹�Ȥ�AS ASSIGNMENT��ץ��դ��ȡ��оݥǡ��ݡ��Ū�ˤ��Υ��㥹�Ȥ�ƤӽФ��褦��Ǥ��ޤ�� 㤨�С�foo.f1��text��Ǥ��Ȥ��ޤ��

INSERT INTO foo (f1) VALUES (42);

integer��text��Ѵ��륭�㥹�Ȥ�AS ASSIGNMENT��ץ��դ��Ƥ��С��嵭��SQLʸ�ϼ¹Բ�ǽ�Ǥ�� ץ��դ��Ƥ��ʤ��С��¹ԤǤ��ޤ�� (��Ū�ˡ��μ�Υ��㥹�Ȥ���㥹���ȸƤФ�Ƥ��ޤ�� )

��㥹�Ȥ�AS IMPLICIT��ץ��դ��ȡ��Ǥ⡢�⤷��ϼ��ˤ��ΤǤ⡢��ƤΥ��ƥ��Ȥǰ��Ū�ˤ��Υ��㥹�Ȥ�ƤӽФ��褦��Ǥ��ޤ�� ʲ��򻲾Ȥ��Ƥ�� ||��text��ΰ��ޤ��Τǡ�

SELECT 'The time is ' || now();

�Ȥ��SQLʸ�ϡ�timestamp��text��Ѵ��륭�㥹�Ȥ�AS IMPLICIT��ץ��դ��Ƥ��Τ߼¹Բ�ǽ�Ǥ�� ץ��դ��Ƥ��ʤ��С��ʲ��Τ褦��Ū�˥��㥹�Ȥ򵭽Ҥ��ɬ�פ��ޤ��

SELECT 'The time is ' || CAST(now() AS text);

(��Ū�ˡ��μ�Υ��㥹�Ȥ���ۥ��㥹���ȸƤФ�Ƥ��ޤ�� )

��ۥ��㥹�Ȥϡ�¿�Ѥ��ʤ��Ǥ�� Ū��㥹�Ȥ��Ѥ��ȡ�PostgreSQL��ޥ�ɤ�פ�̰�̣�˲�ᤷ�Ƥ��ޤ��ˤʤ�ޤ�� ⤷��ϡ�ʣ��β�᤬��ǽ�ʤ��ᡢ��ޥ�ɤ��ɤǤ��ʤ��ʤäƤ��ޤ��ǽ��⤢��ޤ�� и�Ū�ˤϡ�Ʊ��Ū�ʥǡ��ƥ��Υǡ��֤ǡ��ݻ��Ѵ��ǤΤߡ��ۥ��㥹�Ȥ�ƤӽФ��ǽ�ˤ��Τ��ɤ��ˡ�Ȼפ��ޤ�� 㤨�С�int2��int4��ؤΥ��㥹�Ȥϡ��ۥ��㥹�Ȥˤ��Τ��Ǥ��float8��int4��ؤΥ��㥹�Ȥϡ��餯��㥹�ȤΤߤȤ��٤��Ǥ��礦�� text��int4��ؤ��Ѵ��Τ褦�ʡ��ƥ��ۤ��ǡ��Υ��㥹�Ȥϡ��Ū�ˤΤ߻��Ѥ��Τ�Ŭ�ڤǤ��

��㥹�Ȥ��ǽ�ˤ��ˤϡ��Ѵ��ޤ��Ѵ��Υǡ��ͭ��Ƥ��ɬ�פ��ޤ�� ޤ��Х��ʥ�ߴ��륭�㥹�Ȥ��ˤϡ��ѡ��桼��Ǥ��ɬ�פ��ޤ� (�Х��ʥ�ߴ��륭�㥹��Ѵ��äƻ��Ѥ��ȥ��Ф��å��夷�Ƥ��ޤ��ǽ��⤤��Ȥ��顢��¤��դ��ޤ��)��

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sourcetype: ��㥹�Ȥ��Ѵ��Υǡ��̾��Ǥ��
targettype: ��㥹�Ȥ��Ѵ��Υǡ��̾��Ǥ��
funcname(argtypes): ��δؿ��ϡ��㥹�Ȥ�¹Ԥ��뤿��˻��Ѥ��ޤ�� ؿ�̾�ϡ��޽��뤳�Ȥ��Ǥ��ޤ�� ޽��Ƥ��ʤ��硢�ؿ��ϥ��޸��ѥ��鸡��ޤ�� ؿ��η�̤Υǡ��ϥ��㥹�Ȥ��Ѵ��Υǡ��Ȱ��פ��ɬ�פ��ޤ�� ˤĤ��Ƥϸ��ޤ��
WITHOUT FUNCTION: �Ѵ��ǡ��Ѵ��ǡ��ϡ��Х��ʥ�ߴ��뤳�Ȥ򼨤��ޤ�� äơ��㥹�Ȥ�¹Ԥ��Τ˴ؿ��ɬ�פ��ޤ��
AS ASSIGNMENT: ��ƥ��Ȥǡ��Ū�˥��㥹�Ȥ�ƤӽФ��Ȥ��Ǥ��뤳�Ȥ򼨤��ޤ��
AS IMPLICIT: Ǥ�դΥ��ƥ��Ȥǡ��Ū�˥��㥹�Ȥ�ƤӽФ��Ȥ��Ǥ��뤳�Ȥ򼨤��ޤ��

��㥹�Ȥ��ؿ��1��3�Ĥΰ��뤳�Ȥ��Ǥ��ޤ�� 1��ܤΰ��ϥ��㥹�Ȥ��Ѵ��ǡ��Ʊ��Ǥʤ��Фʤ�ޤ�� 2��ܤΰ��ϡ��⤷��С�integer��Ǥʤ��Фʤ餺��Ѵ��η��˴�Ϣ�դ��Ҥ��ޤ�� Ҥ��ʤ��-1��ޤ�� 3��ܤΰ��ϡ��⤷��С�boolean��Ǥʤ��Фʤ餺��㥹�Ȥ��Ū�ʥ��㥹�ȤǤ��true�򡢤��ʳ��Ǥ��false��ޤ�� (��̯�Ǥ��SQL��ͤǤϡ��Ū��㥹�ȤȰ��Ū��㥹�ȤȤδ֤ǰۤʤ뿶�񤤤��׵᤹��礬��ޤ�� ΰ��Ϥ��ʤ��Фʤ�ʤ��ؿ��Ѥ��󶡤��ΤǤ�� ȼ��Υǡ��򤳤�ή��˽��褦��߷פ��뤳�Ȥϴ��ޤ��)

��̡��㥹�Ȥϰۤʤ��Ѵ��Ѵ��Υǡ��ʤ��Фʤ�ޤ�� 2�İʾ�ΰ��Ĵؿ��ǥ��㥹�Ȥ��ϡ��Ѵ��Ѵ��Ȥ�Ʊ��Υǡ��ĥ��㥹�Ȥ��뤳�Ȥ��Ǥ��ޤ�� ϡ��ƥ५��ˤ��Ʒ��ͭ��Ĺ��ؿ��ɽ��뤿��˻��Ѥ��Ƥޤ�� ̾��줿�ؿ��ϡ�2��ܤΰ��Ϳ��줿��Ҥ��ͤǷ��ͤ��뤿��˻��Ѥ��ޤ�� (ʸˡ�塢��Ȥ߹��ߥǡ��Τߤ��Ҥ��Ĥ��Ȥ��Ǥ��ޤ��Τǡ��ε�ǽ��Ѵ��褬�桼��Υǡ��ξ��ˤ��Ω��ޤ�� ˤ��뤿��ˤ��ǵ��Ҥ��Ƥ��ޤ��)

�Ѵ��Ѵ��Υǡ��ۤʤ륭�㥹�Ȥǡ��δؿ��ʣ��ΰ��硢��ϡ��ǡ��¾�Υǡ��ؤ��Ѵ��Ĺ��ζ��1�Ĥ��ˤޤȤ᤿��ΤǤ��뤳�Ȥ�ɽ��ޤ�� ܤ��ʤ��ȡ��Ҥ��Ѥ��뷿�ζ��ϡ��ǽ�˥ǡ��֤��Ѵ��˽��Ҥ�Ŭ�ѤȤ��2�Ĥ��ɬ�פȤʤ�ޤ��

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PostgreSQL 7.3��ΥС��Ǥϡ��ǡ��Ʊ��̾��ǡ��Υǡ��֤��ۤʤ�ǡ��ΰ��1�ļ��ؿ��ϡ��ưŪ�˥��㥹�ȴؿ��Ȥ��Ƥ��ޤ�� δ��ϡ��ޤ�Ƴ��ƥ५��ǥХ��ʥ�ߴ��륭�㥹�Ȥ�ɽ��ǽ�ˤʤä��Ȥˤ�ꡢ�ػߤ��ޤ�� Ȥ߹��ߥ��㥹�ȴؿ��ϡ��ޤ��̿̾��§�˽��äƤ��ޤ�� Ʊ�ͤ�pg_cast��ƥ५��ǥ��㥹�ȤȤ��Ƽ��ɬ�פ��ޤ��

ɬ�פǤϤ��ޤ��󤬡��㥹�Ȥ��ؿ��Ѵ��Υǡ��˰��̿̾��Ȥ��θŤ��˽��³��뤳�Ȥ�侩��ޤ�� ¿��Υ桼��ϴؿ��ͼ��ε�ˡ��Ĥޤ�typename(x)��Ѥ��ƥǡ��Υ��㥹�Ȥ��Ǥ��Ȥ��Ȥ��Ѥ��Ƥ��ޤ�� ε�ˡ�ϥ��㥹�Ȥ��ؿ��ƤӽФ��Ƥ��뤳�Ȥ�¾�ʤ�ޤ�� ä˥��㥹�ȤȤ��ư��äƤ��櫓�ǤϤʤ��ΤǤ�� ȼ��Ѵ��ؿ��̾��δ��˽��äƤ��ʤ��ȡ�¾�Υ桼��ϤȤޤɤ��Ȥˤʤ�ޤ�� PostgreSQL�ϰۤʤ��Ʊ��̾��δؿ��򥪡��С��ɤ��뤳�Ȥ��Ǥ��ޤ��Τǡ��͡��ʷ��餢��Ѵ��跿�ؤ�ʣ��Ѵ��ؿ��Ѵ��η�̾��Ѥ��ƺ��뤳�Ȥ��񤷤��ޤ��

��: ��ˤϾ��ʱ��ޤ�� Τʴؿ��ƤӽФ��ΰ�̣��Τ��pg_cast��Ѥ��礬��뤳�ȤǤ�� ؿ��ƤӽФ�name(x)��ºݤδؿ��˰��פ��name��ǡ��̾��Ǥ��ꡢpg_cast��x�η��餽�η��ؤΥ��㥹�Ȥ��Х��ʥ�ߴ��Ǥ��뤳�Ȥ򼨤��Ƥ��硢��θƤӽФ��Ū��㥹�ȤȤ��ƸƤӽФ��ޤ�� 㳰�ϡ��Х��ʥ�ߴ��㥹�Ȥ򡢼ºݤδؿ��ʤ��ä��Ȥ��Ƥ⡢�ؿ��Τ褦�ʹ�ʸ�ǸƤӽФ��Ȥ��Ǥ��褦�˺��ޤ��

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�ؿ�int4(text)��Ѥ��text��int4��ؤΥ��㥹�Ȥ��ޤ��

CREATE CAST (text AS int4) WITH FUNCTION int4(text);

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CREATE FUNCTION, CREATE TYPE, DROP CAST

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