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/*
* 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. */
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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