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概要 †

* This struct is passed around within the backend to describe the structure
* of tuples.  For tuples coming from on-disk relations, the information is
* collected from the pg_attribute, pg_attrdef, and pg_constraint catalogs.
* Transient row types (such as the result of a join query) have anonymous
* TupleDesc structs that generally omit any constraint info; therefore the
* structure is designed to let the constraints be omitted efficiently.
*
* Note that only user attributes, not system attributes, are mentioned in
* TupleDesc; with the exception that tdhasoid indicates if OID is present.
*
* If the tupdesc is known to correspond to a named rowtype (such as a table's
* rowtype) then tdtypeid identifies that type and tdtypmod is -1.	Otherwise
* tdtypeid is RECORDOID, and tdtypmod can be either -1 for a fully anonymous
* row type, or a value >= 0 to allow the rowtype to be looked up in the
* typcache.c type cache.
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実装 †

  1. nattsを、intとして定義。
  2. attrsを、Form_pg_attributeへのポインタとして定義。
  3. constrを、TupleConstrへのポインタとして定義。
  4. tdtypeidを、Oidとして定義。
  5. tdtypmodを、int32として定義。
  6. tdhasoidを、boolとして定義。

typedef struct tupleDesc {

	int			natts;			/* number of attributes in the tuple */
	Form_pg_attribute *attrs;
	/* attrs[N] is a pointer to the description of Attribute Number N+1 */
	TupleConstr *constr;		/* constraints, or NULL if none */
	Oid			tdtypeid;		/* composite type ID for tuple type */
	int32		tdtypmod;		/* typmod for tuple type */
	bool		tdhasoid;		/* tuple has oid attribute in its header */

} *TupleDesc;

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履歴 †

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コメント †


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