JSON_HB histogram: represent values of BIT() columns in hex always

mysql-test/main/statistics_json.result

@@ -374,23 +374,23 @@ test	t1	f	1	5	0.2000	6.4000	4	JSON_HB	{
   "collected_by": "REPLACED",
   "histogram_hb": [
     {
-      "start": "\u0001",
+      "start_hex": "01",
       "size": 0.28125,
       "ndv": 2
     },
     {
-      "start": "\u0002",
+      "start_hex": "02",
       "size": 0.28125,
       "ndv": 2
     },
     {
-      "start": "\u0004",
+      "start_hex": "04",
       "size": 0.3125,
       "ndv": 1
     },
     {
-      "start": "\u0005",
+      "start_hex": "05",
-      "end": "\u0005",
+      "end_hex": "05",
       "size": 0.125,
       "ndv": 1
     }
@@ -586,28 +586,28 @@ test	t1	f	1	5	0.2000	6.4000	5	JSON_HB	{
   "collected_by": "REPLACED",
   "histogram_hb": [
     {
-      "start": "\u0001",
+      "start_hex": "01",
       "size": 0.125,
       "ndv": 1
     },
     {
-      "start": "\u0002",
+      "start_hex": "02",
       "size": 0.25,
       "ndv": 1
     },
     {
-      "start": "\u0003",
+      "start_hex": "03",
       "size": 0.1875,
       "ndv": 1
     },
     {
-      "start": "\u0004",
+      "start_hex": "04",
       "size": 0.3125,
       "ndv": 1
     },
     {
-      "start": "\u0005",
+      "start_hex": "05",
-      "end": "\u0005",
+      "end_hex": "05",
       "size": 0.125,
       "ndv": 1
     }
@@ -8284,3 +8284,41 @@ analyze select f from t1 where f in (77, 1, 144, 73, 14, 12);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	r_rows	filtered	r_filtered	Extra
 1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	20	20.00	10.00	10.00	Using where
 drop table t1;
+#
+# Test that histograms over BIT fields use hex
+#
+create table t1 (a BIT(64));
+insert into t1 values 
+(x'01'),(x'10'),(x'BE562B1A99001918');
+set histogram_type= JSON_HB;
+analyze table t1 persistent for all;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	Engine-independent statistics collected
+test.t1	analyze	status	OK
+select histogram
+from mysql.column_stats where table_name='t1' and db_name=database();
+histogram
+{
+  "target_histogram_size": 254,
+  "collected_at": "REPLACED",
+  "collected_by": "REPLACED",
+  "histogram_hb": [
+    {
+      "start_hex": "0000000000000001",
+      "size": 0.333333333,
+      "ndv": 1
+    },
+    {
+      "start_hex": "0000000000000010",
+      "size": 0.333333333,
+      "ndv": 1
+    },
+    {
+      "start_hex": "BE562B1A99001918",
+      "end_hex": "BE562B1A99001918",
+      "size": 0.333333333,
+      "ndv": 1
+    }
+  ]
+}
+drop table t1;

mysql-test/main/statistics_json.test

@@ -445,3 +445,18 @@ analyze table t1 persistent for all;
 analyze select f from t1 where f in (77, 1, 144, 73, 14, 12);
 drop table t1;
 
+
+--echo #
+--echo # Test that histograms over BIT fields use hex
+--echo #
+create table t1 (a BIT(64));
+insert into t1 values 
+  (x'01'),(x'10'),(x'BE562B1A99001918');
+set histogram_type= JSON_HB;
+analyze table t1 persistent for all;
+--source include/json_hb_histogram.inc
+select histogram
+from mysql.column_stats where table_name='t1' and db_name=database();
+
+drop table t1;
+

sql/opt_histogram_json.cc

@@ -122,6 +122,12 @@ class Histogram_json_builder : public Histogram_builder
   /* Number of the buckets already collected */
   uint n_buckets_collected;
 
+  /*
+    TRUE means do not try to represent values as UTF-8 text in histogram
+    storage. Use start_hex/end_hex for all values.
+  */
+  bool force_binary;
+
   /* Data about the bucket we are filling now */
   struct CurBucket
   {
@@ -135,6 +141,7 @@ class Histogram_json_builder : public Histogram_builder
 
   /* Used to create the JSON representation of the histogram. */
   Json_writer writer;
+
 public:
 
   Histogram_json_builder(Histogram_json_hb *hist, Field *col, uint col_len,
@@ -155,6 +162,7 @@ public:
     n_buckets_collected= 0;
     bucket.ndv= 0;
     bucket.size= 0;
+    force_binary= (col->type() == MYSQL_TYPE_BIT);
 
     writer.start_object();
     append_histogram_params();
@@ -244,13 +252,17 @@ private:
 
     // Escape the value for JSON
     StringBuffer<MAX_FIELD_WIDTH> escaped_val;
-    int rc= json_escape_to_string(str, &escaped_val);
+    int rc= JSON_ERROR_ILLEGAL_SYMBOL;
+    if (!force_binary)
+    {
+      rc= json_escape_to_string(str, &escaped_val);
       if (!rc)
       {
         writer.add_member(is_start? "start": "end");
         writer.add_str(escaped_val.c_ptr_safe());
         return false;
       }
+    }
     if (rc == JSON_ERROR_ILLEGAL_SYMBOL)
     {
       escaped_val.set_hex(val.ptr(), val.length());