commit 78d0188fcf4c01fa824e6f09a8026629eaa725ef
Author: Alexander Korotkov <akorotkov@postgresql.org>
Date:   Wed Aug 7 23:41:58 2019 +0300

    Adjust string comparison in jsonpath
    
    We have implemented jsonpath string comparison using default database locale.
    However, standard requires us to compare Unicode codepoints.  This commit
    implements that, but for performance reasons we still use per-byte comparison
    for "==" operator.  Thus, for consistency other comparison operators do per-byte
    comparison if Unicode codepoints appear to be equal.
    
    In some edge cases, when same Unicode codepoints have different binary
    representations in database encoding, we diverge standard to achieve better
    performance of "==" operator.  In future to implement strict standard
    conformance, we can do normalization of input JSON strings.
    
    Original patch was written by Nikita Glukhov, rewritten by me.
    
    Reported-by: Markus Winand
    Discussion: https://postgr.es/m/8B7FA3B4-328D-43D7-95A8-37B8891B8C78%40winand.at
    Author: Nikita Glukhov, Alexander Korotkov
    Backpatch-through: 12

diff --git a/src/backend/utils/adt/jsonpath_exec.c b/src/backend/utils/adt/jsonpath_exec.c
index 293d6da027c..4a0de4fe95a 100644
--- a/src/backend/utils/adt/jsonpath_exec.c
+++ b/src/backend/utils/adt/jsonpath_exec.c
@@ -1980,6 +1980,73 @@ executeComparison(JsonPathItem *cmp, JsonbValue *lv, JsonbValue *rv, void *p)
 	return compareItems(cmp->type, lv, rv);
 }
 
+/*
+ * Perform per-byte comparison of two strings.
+ */
+static int
+binaryCompareStrings(const char *s1, int len1,
+					 const char *s2, int len2)
+{
+	int			cmp;
+
+	cmp = memcmp(s1, s2, Min(len1, len2));
+
+	if (cmp != 0)
+		return cmp;
+
+	if (len1 == len2)
+		return 0;
+
+	return len1 < len2 ? -1 : 1;
+}
+
+/*
+ * Compare two strings in the current server encoding using Unicode codepoint
+ * collation.
+ */
+static int
+compareStrings(const char *mbstr1, int mblen1,
+			   const char *mbstr2, int mblen2)
+{
+	if (GetDatabaseEncoding() == PG_SQL_ASCII ||
+		GetDatabaseEncoding() == PG_UTF8)
+	{
+		/*
+		 * It's known property of UTF-8 strings that their per-byte comparison
+		 * result matches codepoints comparison result.  ASCII can be
+		 * considered as special case of UTF-8.
+		 */
+		return binaryCompareStrings(mbstr1, mblen1, mbstr2, mblen2);
+	}
+	else
+	{
+		/* We have to convert other encodings to UTF-8 first, then compare. */
+		char	   *utf8str1 = pg_server_to_any(mbstr1, mblen1, PG_UTF8),
+				   *utf8str2 = pg_server_to_any(mbstr2, mblen2, PG_UTF8);
+		int			cmp;
+
+		cmp = binaryCompareStrings(utf8str1, strlen(utf8str1),
+								   utf8str2, strlen(utf8str2));
+
+		pfree(utf8str1);
+		pfree(utf8str2);
+
+		/*
+		 * When all Unicode codepoints are equal, return result of binary
+		 * comparison.  In some edge cases, same characters may have different
+		 * representations in encoding.  Then our behavior could diverge from
+		 * standard.  However, that allow us to do simple binary comparison
+		 * for "==" operator, which is performance critical in typical cases.
+		 * In future to implement strict standard conformance, we can do
+		 * normalization of input JSON strings.
+		 */
+		if (cmp == 0)
+			return binaryCompareStrings(mbstr1, mblen1, mbstr2, mblen2);
+		else
+			return cmp;
+	}
+}
+
 /*
  * Compare two SQL/JSON items using comparison operation 'op'.
  */
@@ -2022,9 +2089,8 @@ compareItems(int32 op, JsonbValue *jb1, JsonbValue *jb2)
 						   jb2->val.string.val,
 						   jb1->val.string.len) ? jpbFalse : jpbTrue;
 
-			cmp = varstr_cmp(jb1->val.string.val, jb1->val.string.len,
-							 jb2->val.string.val, jb2->val.string.len,
-							 DEFAULT_COLLATION_OID);
+			cmp = compareStrings(jb1->val.string.val, jb1->val.string.len,
+								 jb2->val.string.val, jb2->val.string.len);
 			break;
 
 		case jbvBinary:
diff --git a/src/test/regress/expected/jsonb_jsonpath.out b/src/test/regress/expected/jsonb_jsonpath.out
index 31a871af028..0202667a1f7 100644
--- a/src/test/regress/expected/jsonb_jsonpath.out
+++ b/src/test/regress/expected/jsonb_jsonpath.out
@@ -1833,3 +1833,166 @@ SELECT jsonb_path_match('[{"a": 1}, {"a": 2}]', '$[*].a > 1');
  t
 (1 row)
 
+-- test string comparison (Unicode codepoint collation)
+WITH str(j, num) AS
+(
+	SELECT jsonb_build_object('s', s), num
+	FROM unnest('{"", "a", "ab", "abc", "abcd", "b", "A", "AB", "ABC", "ABc", "ABcD", "B"}'::text[]) WITH ORDINALITY AS a(s, num)
+)
+SELECT
+	s1.j, s2.j,
+	jsonb_path_query_first(s1.j, '$.s < $s', vars => s2.j) lt,
+	jsonb_path_query_first(s1.j, '$.s <= $s', vars => s2.j) le,
+	jsonb_path_query_first(s1.j, '$.s == $s', vars => s2.j) eq,
+	jsonb_path_query_first(s1.j, '$.s >= $s', vars => s2.j) ge,
+	jsonb_path_query_first(s1.j, '$.s > $s', vars => s2.j) gt
+FROM str s1, str s2
+ORDER BY s1.num, s2.num;
+       j       |       j       |  lt   |  le   |  eq   |  ge   |  gt   
+---------------+---------------+-------+-------+-------+-------+-------
+ {"s": ""}     | {"s": ""}     | false | true  | true  | true  | false
+ {"s": ""}     | {"s": "a"}    | true  | true  | false | false | false
+ {"s": ""}     | {"s": "ab"}   | true  | true  | false | false | false
+ {"s": ""}     | {"s": "abc"}  | true  | true  | false | false | false
+ {"s": ""}     | {"s": "abcd"} | true  | true  | false | false | false
+ {"s": ""}     | {"s": "b"}    | true  | true  | false | false | false
+ {"s": ""}     | {"s": "A"}    | true  | true  | false | false | false
+ {"s": ""}     | {"s": "AB"}   | true  | true  | false | false | false
+ {"s": ""}     | {"s": "ABC"}  | true  | true  | false | false | false
+ {"s": ""}     | {"s": "ABc"}  | true  | true  | false | false | false
+ {"s": ""}     | {"s": "ABcD"} | true  | true  | false | false | false
+ {"s": ""}     | {"s": "B"}    | true  | true  | false | false | false
+ {"s": "a"}    | {"s": ""}     | false | false | false | true  | true
+ {"s": "a"}    | {"s": "a"}    | false | true  | true  | true  | false
+ {"s": "a"}    | {"s": "ab"}   | true  | true  | false | false | false
+ {"s": "a"}    | {"s": "abc"}  | true  | true  | false | false | false
+ {"s": "a"}    | {"s": "abcd"} | true  | true  | false | false | false
+ {"s": "a"}    | {"s": "b"}    | true  | true  | false | false | false
+ {"s": "a"}    | {"s": "A"}    | false | false | false | true  | true
+ {"s": "a"}    | {"s": "AB"}   | false | false | false | true  | true
+ {"s": "a"}    | {"s": "ABC"}  | false | false | false | true  | true
+ {"s": "a"}    | {"s": "ABc"}  | false | false | false | true  | true
+ {"s": "a"}    | {"s": "ABcD"} | false | false | false | true  | true
+ {"s": "a"}    | {"s": "B"}    | false | false | false | true  | true
+ {"s": "ab"}   | {"s": ""}     | false | false | false | true  | true
+ {"s": "ab"}   | {"s": "a"}    | false | false | false | true  | true
+ {"s": "ab"}   | {"s": "ab"}   | false | true  | true  | true  | false
+ {"s": "ab"}   | {"s": "abc"}  | true  | true  | false | false | false
+ {"s": "ab"}   | {"s": "abcd"} | true  | true  | false | false | false
+ {"s": "ab"}   | {"s": "b"}    | true  | true  | false | false | false
+ {"s": "ab"}   | {"s": "A"}    | false | false | false | true  | true
+ {"s": "ab"}   | {"s": "AB"}   | false | false | false | true  | true
+ {"s": "ab"}   | {"s": "ABC"}  | false | false | false | true  | true
+ {"s": "ab"}   | {"s": "ABc"}  | false | false | false | true  | true
+ {"s": "ab"}   | {"s": "ABcD"} | false | false | false | true  | true
+ {"s": "ab"}   | {"s": "B"}    | false | false | false | true  | true
+ {"s": "abc"}  | {"s": ""}     | false | false | false | true  | true
+ {"s": "abc"}  | {"s": "a"}    | false | false | false | true  | true
+ {"s": "abc"}  | {"s": "ab"}   | false | false | false | true  | true
+ {"s": "abc"}  | {"s": "abc"}  | false | true  | true  | true  | false
+ {"s": "abc"}  | {"s": "abcd"} | true  | true  | false | false | false
+ {"s": "abc"}  | {"s": "b"}    | true  | true  | false | false | false
+ {"s": "abc"}  | {"s": "A"}    | false | false | false | true  | true
+ {"s": "abc"}  | {"s": "AB"}   | false | false | false | true  | true
+ {"s": "abc"}  | {"s": "ABC"}  | false | false | false | true  | true
+ {"s": "abc"}  | {"s": "ABc"}  | false | false | false | true  | true
+ {"s": "abc"}  | {"s": "ABcD"} | false | false | false | true  | true
+ {"s": "abc"}  | {"s": "B"}    | false | false | false | true  | true
+ {"s": "abcd"} | {"s": ""}     | false | false | false | true  | true
+ {"s": "abcd"} | {"s": "a"}    | false | false | false | true  | true
+ {"s": "abcd"} | {"s": "ab"}   | false | false | false | true  | true
+ {"s": "abcd"} | {"s": "abc"}  | false | false | false | true  | true
+ {"s": "abcd"} | {"s": "abcd"} | false | true  | true  | true  | false
+ {"s": "abcd"} | {"s": "b"}    | true  | true  | false | false | false
+ {"s": "abcd"} | {"s": "A"}    | false | false | false | true  | true
+ {"s": "abcd"} | {"s": "AB"}   | false | false | false | true  | true
+ {"s": "abcd"} | {"s": "ABC"}  | false | false | false | true  | true
+ {"s": "abcd"} | {"s": "ABc"}  | false | false | false | true  | true
+ {"s": "abcd"} | {"s": "ABcD"} | false | false | false | true  | true
+ {"s": "abcd"} | {"s": "B"}    | false | false | false | true  | true
+ {"s": "b"}    | {"s": ""}     | false | false | false | true  | true
+ {"s": "b"}    | {"s": "a"}    | false | false | false | true  | true
+ {"s": "b"}    | {"s": "ab"}   | false | false | false | true  | true
+ {"s": "b"}    | {"s": "abc"}  | false | false | false | true  | true
+ {"s": "b"}    | {"s": "abcd"} | false | false | false | true  | true
+ {"s": "b"}    | {"s": "b"}    | false | true  | true  | true  | false
+ {"s": "b"}    | {"s": "A"}    | false | false | false | true  | true
+ {"s": "b"}    | {"s": "AB"}   | false | false | false | true  | true
+ {"s": "b"}    | {"s": "ABC"}  | false | false | false | true  | true
+ {"s": "b"}    | {"s": "ABc"}  | false | false | false | true  | true
+ {"s": "b"}    | {"s": "ABcD"} | false | false | false | true  | true
+ {"s": "b"}    | {"s": "B"}    | false | false | false | true  | true
+ {"s": "A"}    | {"s": ""}     | false | false | false | true  | true
+ {"s": "A"}    | {"s": "a"}    | true  | true  | false | false | false
+ {"s": "A"}    | {"s": "ab"}   | true  | true  | false | false | false
+ {"s": "A"}    | {"s": "abc"}  | true  | true  | false | false | false
+ {"s": "A"}    | {"s": "abcd"} | true  | true  | false | false | false
+ {"s": "A"}    | {"s": "b"}    | true  | true  | false | false | false
+ {"s": "A"}    | {"s": "A"}    | false | true  | true  | true  | false
+ {"s": "A"}    | {"s": "AB"}   | true  | true  | false | false | false
+ {"s": "A"}    | {"s": "ABC"}  | true  | true  | false | false | false
+ {"s": "A"}    | {"s": "ABc"}  | true  | true  | false | false | false
+ {"s": "A"}    | {"s": "ABcD"} | true  | true  | false | false | false
+ {"s": "A"}    | {"s": "B"}    | true  | true  | false | false | false
+ {"s": "AB"}   | {"s": ""}     | false | false | false | true  | true
+ {"s": "AB"}   | {"s": "a"}    | true  | true  | false | false | false
+ {"s": "AB"}   | {"s": "ab"}   | true  | true  | false | false | false
+ {"s": "AB"}   | {"s": "abc"}  | true  | true  | false | false | false
+ {"s": "AB"}   | {"s": "abcd"} | true  | true  | false | false | false
+ {"s": "AB"}   | {"s": "b"}    | true  | true  | false | false | false
+ {"s": "AB"}   | {"s": "A"}    | false | false | false | true  | true
+ {"s": "AB"}   | {"s": "AB"}   | false | true  | true  | true  | false
+ {"s": "AB"}   | {"s": "ABC"}  | true  | true  | false | false | false
+ {"s": "AB"}   | {"s": "ABc"}  | true  | true  | false | false | false
+ {"s": "AB"}   | {"s": "ABcD"} | true  | true  | false | false | false
+ {"s": "AB"}   | {"s": "B"}    | true  | true  | false | false | false
+ {"s": "ABC"}  | {"s": ""}     | false | false | false | true  | true
+ {"s": "ABC"}  | {"s": "a"}    | true  | true  | false | false | false
+ {"s": "ABC"}  | {"s": "ab"}   | true  | true  | false | false | false
+ {"s": "ABC"}  | {"s": "abc"}  | true  | true  | false | false | false
+ {"s": "ABC"}  | {"s": "abcd"} | true  | true  | false | false | false
+ {"s": "ABC"}  | {"s": "b"}    | true  | true  | false | false | false
+ {"s": "ABC"}  | {"s": "A"}    | false | false | false | true  | true
+ {"s": "ABC"}  | {"s": "AB"}   | false | false | false | true  | true
+ {"s": "ABC"}  | {"s": "ABC"}  | false | true  | true  | true  | false
+ {"s": "ABC"}  | {"s": "ABc"}  | true  | true  | false | false | false
+ {"s": "ABC"}  | {"s": "ABcD"} | true  | true  | false | false | false
+ {"s": "ABC"}  | {"s": "B"}    | true  | true  | false | false | false
+ {"s": "ABc"}  | {"s": ""}     | false | false | false | true  | true
+ {"s": "ABc"}  | {"s": "a"}    | true  | true  | false | false | false
+ {"s": "ABc"}  | {"s": "ab"}   | true  | true  | false | false | false
+ {"s": "ABc"}  | {"s": "abc"}  | true  | true  | false | false | false
+ {"s": "ABc"}  | {"s": "abcd"} | true  | true  | false | false | false
+ {"s": "ABc"}  | {"s": "b"}    | true  | true  | false | false | false
+ {"s": "ABc"}  | {"s": "A"}    | false | false | false | true  | true
+ {"s": "ABc"}  | {"s": "AB"}   | false | false | false | true  | true
+ {"s": "ABc"}  | {"s": "ABC"}  | false | false | false | true  | true
+ {"s": "ABc"}  | {"s": "ABc"}  | false | true  | true  | true  | false
+ {"s": "ABc"}  | {"s": "ABcD"} | true  | true  | false | false | false
+ {"s": "ABc"}  | {"s": "B"}    | true  | true  | false | false | false
+ {"s": "ABcD"} | {"s": ""}     | false | false | false | true  | true
+ {"s": "ABcD"} | {"s": "a"}    | true  | true  | false | false | false
+ {"s": "ABcD"} | {"s": "ab"}   | true  | true  | false | false | false
+ {"s": "ABcD"} | {"s": "abc"}  | true  | true  | false | false | false
+ {"s": "ABcD"} | {"s": "abcd"} | true  | true  | false | false | false
+ {"s": "ABcD"} | {"s": "b"}    | true  | true  | false | false | false
+ {"s": "ABcD"} | {"s": "A"}    | false | false | false | true  | true
+ {"s": "ABcD"} | {"s": "AB"}   | false | false | false | true  | true
+ {"s": "ABcD"} | {"s": "ABC"}  | false | false | false | true  | true
+ {"s": "ABcD"} | {"s": "ABc"}  | false | false | false | true  | true
+ {"s": "ABcD"} | {"s": "ABcD"} | false | true  | true  | true  | false
+ {"s": "ABcD"} | {"s": "B"}    | true  | true  | false | false | false
+ {"s": "B"}    | {"s": ""}     | false | false | false | true  | true
+ {"s": "B"}    | {"s": "a"}    | true  | true  | false | false | false
+ {"s": "B"}    | {"s": "ab"}   | true  | true  | false | false | false
+ {"s": "B"}    | {"s": "abc"}  | true  | true  | false | false | false
+ {"s": "B"}    | {"s": "abcd"} | true  | true  | false | false | false
+ {"s": "B"}    | {"s": "b"}    | true  | true  | false | false | false
+ {"s": "B"}    | {"s": "A"}    | false | false | false | true  | true
+ {"s": "B"}    | {"s": "AB"}   | false | false | false | true  | true
+ {"s": "B"}    | {"s": "ABC"}  | false | false | false | true  | true
+ {"s": "B"}    | {"s": "ABc"}  | false | false | false | true  | true
+ {"s": "B"}    | {"s": "ABcD"} | false | false | false | true  | true
+ {"s": "B"}    | {"s": "B"}    | false | true  | true  | true  | false
+(144 rows)
+
diff --git a/src/test/regress/sql/jsonb_jsonpath.sql b/src/test/regress/sql/jsonb_jsonpath.sql
index 733fbd4e0d0..e7629fb7f9d 100644
--- a/src/test/regress/sql/jsonb_jsonpath.sql
+++ b/src/test/regress/sql/jsonb_jsonpath.sql
@@ -387,3 +387,19 @@ SELECT jsonb_path_match('[true, true]', '$[*]', silent => false);
 SELECT jsonb '[{"a": 1}, {"a": 2}]' @@ '$[*].a > 1';
 SELECT jsonb '[{"a": 1}, {"a": 2}]' @@ '$[*].a > 2';
 SELECT jsonb_path_match('[{"a": 1}, {"a": 2}]', '$[*].a > 1');
+
+-- test string comparison (Unicode codepoint collation)
+WITH str(j, num) AS
+(
+	SELECT jsonb_build_object('s', s), num
+	FROM unnest('{"", "a", "ab", "abc", "abcd", "b", "A", "AB", "ABC", "ABc", "ABcD", "B"}'::text[]) WITH ORDINALITY AS a(s, num)
+)
+SELECT
+	s1.j, s2.j,
+	jsonb_path_query_first(s1.j, '$.s < $s', vars => s2.j) lt,
+	jsonb_path_query_first(s1.j, '$.s <= $s', vars => s2.j) le,
+	jsonb_path_query_first(s1.j, '$.s == $s', vars => s2.j) eq,
+	jsonb_path_query_first(s1.j, '$.s >= $s', vars => s2.j) ge,
+	jsonb_path_query_first(s1.j, '$.s > $s', vars => s2.j) gt
+FROM str s1, str s2
+ORDER BY s1.num, s2.num;