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db_include/access/attmap.h

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+/*-------------------------------------------------------------------------
+ *
+ * attmap.h
+ *	  Definitions for PostgreSQL attribute mappings
+ *
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/access/attmap.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef ATTMAP_H
+#define ATTMAP_H
+
+#include "access/attnum.h"
+#include "access/tupdesc.h"
+
+/*
+ * Attribute mapping structure
+ *
+ * This maps attribute numbers between a pair of relations, designated
+ * 'input' and 'output' (most typically inheritance parent and child
+ * relations), whose common columns may have different attribute numbers.
+ * Such difference may arise due to the columns being ordered differently
+ * in the two relations or the two relations having dropped columns at
+ * different positions.
+ *
+ * 'maplen' is set to the number of attributes of the 'output' relation,
+ * taking into account any of its dropped attributes, with the corresponding
+ * elements of the 'attnums' array set to 0.
+ */
+typedef struct AttrMap
+{
+	AttrNumber *attnums;
+	int			maplen;
+} AttrMap;
+
+extern AttrMap *make_attrmap(int maplen);
+extern void free_attrmap(AttrMap *map);
+
+/* Conversion routines to build mappings */
+extern AttrMap *build_attrmap_by_name(TupleDesc indesc,
+									  TupleDesc outdesc);
+extern AttrMap *build_attrmap_by_name_if_req(TupleDesc indesc,
+											 TupleDesc outdesc);
+extern AttrMap *build_attrmap_by_position(TupleDesc indesc,
+										  TupleDesc outdesc,
+										  const char *msg);
+
+#endif							/* ATTMAP_H */