Fix for bug 3389327: query deparse issue

Origin of this bug was XC planner trying to identify the keyword "FROM"
in a query during reconstruction of an ORDER BY query.

The trick here is to replace "FROM" in the aliases generated by query deparsing
by "_FROM_" to avoid having query reconstruction look for aliases instead of
real FROM clauses.

The new algorithm in place in XC planner is able to rebuild query aliases
to more consistent names even in multiple places.

This fixes the regression test date.

1 files changed, 78 insertions, 6 deletions

diff --git a/src/backend/pgxc/plan/planner.c b/src/backend/pgxc/plan/planner.c
index 83e08be10f..67a2a8c32f 100644
--- a/src/backend/pgxc/plan/planner.c
+++ b/src/backend/pgxc/plan/planner.c
@@ -176,12 +176,12 @@ static bool contains_temp_tables(List *rtable);
 static bool contains_only_pg_catalog(List *rtable);
 
 /*
- * Find position of specified substring in the string
+ * Find nth position of specified substring in the string
  * All non-printable symbols of str treated as spaces, all letters as uppercase
  * Returns pointer to the beginning of the substring or NULL
  */
 static char *
-strpos(char *str, char *substr)
+strpos(char *str, char *substr, int n_pos)
 {
 	char		copy[strlen(str) + 1];
 	char	   *src = str;
@@ -189,7 +189,7 @@ strpos(char *str, char *substr)
 
 	/*
 	 * Initialize mutable copy, converting letters to uppercase and
-	 * various witespace characters to spaces
+	 * various whitespace characters to spaces
 	 */
 	while (*src)
 	{
@@ -202,11 +202,64 @@ strpos(char *str, char *substr)
 			*dst++ = toupper(*src++);
 	}
 	*dst = '\0';
+
 	dst = strstr(copy, substr);
+
+	if (n_pos != 1)
+		dst = strpos(dst + strlen(substr), substr, n_pos - 1);
+
 	return dst ? str + (dst - copy) : NULL;
 }
 
 /*
+ * Convert input string characters into uppercases and
+ * replace "orig" string by "replace" string in given string input
+ * Result has to be freed after calling this function.
+ */
+static char *
+strreplace(char *str, char *orig, char *replace, int *replace_cnt)
+{
+	char		copy[strlen(str) + 1];
+	char	   *src = str;
+	char	   *dst = copy;
+	char	   *buffer = NULL;
+
+	*replace_cnt = 0;
+
+	/* Convert input into correct format with uppercases */
+	while (*src)
+	{
+		if (isspace(*src))
+		{
+			src++;
+			*dst++ = ' ';
+		}
+		else
+			*dst++ = toupper(*src++);
+	}
+	*dst = '\0';
+
+	/* We are sure there is a least 1 replacement */
+	buffer = pstrdup(copy);
+
+	/* Then replace each occurence */
+	while ((dst = strstr(buffer, orig)))
+	{
+		int	strdiff = strlen(str) - strlen(dst);
+
+		(*replace_cnt)++;
+		buffer = (char *) repalloc(buffer, strlen(str) +
+								   (*replace_cnt) * (strlen(replace) - strlen(orig) + 1));
+
+		strncpy(buffer, buffer, strdiff);
+		buffer[strdiff] = '\0';
+		sprintf(buffer + strdiff, "%s%s", replace, dst + strlen(orig));
+	}
+
+	return buffer;
+}
+
+/*
  * True if both lists contain only one node and are the same
  */
 static bool
@@ -2155,6 +2208,7 @@ reconstruct_step_query(List *rtable, bool has_order_by, List *extra_sort,
 	ListCell   *l;
 	StringInfo	buf = makeStringInfo();
 	char	   *sql_from;
+	int			count_from = 1;
 
 	context = deparse_context_for_planstate((Node *) step, NULL, rtable);
 	useprefix = list_length(rtable) > 1;
@@ -2177,7 +2231,25 @@ reconstruct_step_query(List *rtable, bool has_order_by, List *extra_sort,
 		appendStringInfoString(buf, exprstr);
 
 		if (tle->resname != NULL)
-			appendStringInfo(buf, " AS %s", quote_identifier(tle->resname));
+		{
+			/*
+			 * Check if relation aliases are using keyword FROM
+			 * If yes, replace that with _FROM_ to avoid conflicts with
+			 * ORDER BY query reconstruction below.
+			 */
+			if (strpos((char *)quote_identifier(tle->resname), " FROM ", 1))
+			{
+				char   *buffer;
+				int		cnt;
+				buffer = strreplace((char *)quote_identifier(tle->resname),
+									" FROM ", "_FROM_", &cnt);
+				appendStringInfo(buf, " AS %s", buffer);
+				pfree(buffer);
+				count_from += cnt;
+			}
+			else
+				appendStringInfo(buf, " AS %s", quote_identifier(tle->resname));
+		}
 	}
 
 	/*
@@ -2187,7 +2259,7 @@ reconstruct_step_query(List *rtable, bool has_order_by, List *extra_sort,
 	 * Do not handle the case if " FROM " we found is not a "FROM" keyword, but,
 	 * for example, a part of string constant.
 	 */
-	sql_from = strpos(step->sql_statement, " FROM ");
+	sql_from = strpos(step->sql_statement, " FROM ", count_from++);
 	if (sql_from)
 	{
 		/*
@@ -2292,7 +2364,7 @@ fetch_ctid_of(Plan *subtree, RowMarkClause *rmc)
 		 * TODO Find if the table is referenced by the step query
 		 */
 
-		char *from_sql = strpos(step->sql_statement, " FROM ");
+		char *from_sql = strpos(step->sql_statement, " FROM ", 1);
 		if (from_sql)
 		{
 			StringInfoData buf;