Fix incorrect error reporting for duplicate data in \crosstabview.

\crosstabview's complaint about multiple entries for the same crosstab
cell quoted the wrong row and/or column values.  It would accidentally
appear to work if the data had been in strcmp() order to start with,
which probably explains how we missed noticing this during development.

This could be fixed in more than one way, but the way I chose was to
hang onto both result pointers from bsearch() and use those to get at
the value names.

In passing, avoid casting away const in the bsearch comparison functions.
No bug there, just poor style.

Per bug #14476 from Tomonari Katsumata.  Back-patch to 9.6 where
\crosstabview was introduced.

Report: https://postgr.es/m/20161225021519.10139.45460@wrigleys.postgresql.org

src/bin/psql/crosstabview.c

@@ -352,7 +352,8 @@ printCrosstab(const PGresult *results,
 	{
 		int			row_number;
 		int			col_number;
-		pivot_field *p;
+		pivot_field *rp,
+				   *cp;
 		pivot_field elt;
 
 		/* Find target row */
@@ -360,13 +361,13 @@ printCrosstab(const PGresult *results,
 			elt.name = PQgetvalue(results, rn, field_for_rows);
 		else
 			elt.name = NULL;
-		p = (pivot_field *) bsearch(&elt,
+		rp = (pivot_field *) bsearch(&elt,
 									 piv_rows,
 									 num_rows,
 									 sizeof(pivot_field),
 									 pivotFieldCompare);
-		Assert(p != NULL);
-		row_number = p->rank;
+		Assert(rp != NULL);
+		row_number = rp->rank;
 
 		/* Find target column */
 		if (!PQgetisnull(results, rn, field_for_columns))
@@ -374,13 +375,13 @@ printCrosstab(const PGresult *results,
 		else
 			elt.name = NULL;
 
-		p = (pivot_field *) bsearch(&elt,
+		cp = (pivot_field *) bsearch(&elt,
 									 piv_columns,
 									 num_columns,
 									 sizeof(pivot_field),
 									 pivotFieldCompare);
-		Assert(p != NULL);
-		col_number = p->rank;
+		Assert(cp != NULL);
+		col_number = cp->rank;
 
 		/* Place value into cell */
 		if (col_number >= 0 && row_number >= 0)
@@ -396,10 +397,10 @@ printCrosstab(const PGresult *results,
 			if (cont.cells[idx] != NULL)
 			{
 				psql_error("\\crosstabview: query result contains multiple data values for row \"%s\", column \"%s\"\n",
-					  piv_rows[row_number].name ? piv_rows[row_number].name :
-						   popt.nullPrint ? popt.nullPrint : "(null)",
-				piv_columns[col_number].name ? piv_columns[col_number].name :
-						   popt.nullPrint ? popt.nullPrint : "(null)");
+						   rp->name ? rp->name :
+						   (popt.nullPrint ? popt.nullPrint : "(null)"),
+						   cp->name ? cp->name :
+						   (popt.nullPrint ? popt.nullPrint : "(null)"));
 				goto error;
 			}
 
@@ -694,8 +695,8 @@ indexOfColumn(char *arg, const PGresult *res)
 static int
 pivotFieldCompare(const void *a, const void *b)
 {
-	pivot_field *pa = (pivot_field *) a;
-	pivot_field *pb = (pivot_field *) b;
+	const pivot_field *pa = (const pivot_field *) a;
+	const pivot_field *pb = (const pivot_field *) b;
 
 	/* test null values */
 	if (!pb->name)
@@ -704,12 +705,11 @@ pivotFieldCompare(const void *a, const void *b)
 		return 1;
 
 	/* non-null values */
-	return strcmp(((pivot_field *) a)->name,
-				  ((pivot_field *) b)->name);
+	return strcmp(pa->name, pb->name);
 }
 
 static int
 rankCompare(const void *a, const void *b)
 {
-	return *((int *) a) - *((int *) b);
+	return *((const int *) a) - *((const int *) b);
 }

src/test/regress/expected/psql_crosstab.out

@@ -201,3 +201,16 @@ SELECT a,a,1 FROM generate_series(1,3000) AS a
 SELECT 1 \crosstabview
 \crosstabview: query must return at least three columns
 DROP TABLE ctv_data;
+-- check error reporting (bug #14476)
+CREATE TABLE ctv_data (x int, y int, v text);
+INSERT INTO ctv_data SELECT 1, x, '*' || x FROM generate_series(1,10) x;
+SELECT * FROM ctv_data \crosstabview
+ x | 1  | 2  | 3  | 4  | 5  | 6  | 7  | 8  | 9  | 10  
+---+----+----+----+----+----+----+----+----+----+-----
+ 1 | *1 | *2 | *3 | *4 | *5 | *6 | *7 | *8 | *9 | *10
+(1 row)
+
+INSERT INTO ctv_data VALUES (1, 10, '*'); -- duplicate data to cause error
+SELECT * FROM ctv_data \crosstabview
+\crosstabview: query result contains multiple data values for row "1", column "10"
+DROP TABLE ctv_data;

src/test/regress/sql/psql_crosstab.sql

@@ -111,3 +111,14 @@ SELECT a,a,1 FROM generate_series(1,3000) AS a
 SELECT 1 \crosstabview
 
 DROP TABLE ctv_data;
+
+-- check error reporting (bug #14476)
+CREATE TABLE ctv_data (x int, y int, v text);
+
+INSERT INTO ctv_data SELECT 1, x, '*' || x FROM generate_series(1,10) x;
+SELECT * FROM ctv_data \crosstabview
+
+INSERT INTO ctv_data VALUES (1, 10, '*'); -- duplicate data to cause error
+SELECT * FROM ctv_data \crosstabview
+
+DROP TABLE ctv_data;