get wrong NDV when to merge global stats without async

[hawkingrei]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

CREATE TABLE `t1` (
  `emp_id` int(11) NOT NULL,
  `emp_name` varchar(25) NOT NULL,
  `salary` int(11) NOT NULL,
  `dept_id` int(11) NOT NULL,
  PRIMARY KEY (`emp_id`) /*T![clustered_index] NONCLUSTERED */
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin
PARTITION BY RANGE (`emp_id`)
(PARTITION `p0` VALUES LESS THAN (1000),
 PARTITION `p1` VALUES LESS THAN (4000),
 PARTITION `p2` VALUES LESS THAN (12000),
 PARTITION `p3` VALUES LESS THAN (16000),
 PARTITION `p4` VALUES LESS THAN (20000),
 PARTITION `p5` VALUES LESS THAN (25000),
 PARTITION `p6` VALUES LESS THAN (30000),
 PARTITION `p7` VALUES LESS THAN (35000),
 PARTITION `p8` VALUES LESS THAN (40000),
 PARTITION `p9` VALUES LESS THAN (45000),
 PARTITION `p10` VALUES LESS THAN (50000),
 PARTITION `p11` VALUES LESS THAN (55000),
 PARTITION `p12` VALUES LESS THAN (65000),
 PARTITION `p13` VALUES LESS THAN (75000),
 PARTITION `p14` VALUES LESS THAN (85000),
 PARTITION `p15` VALUES LESS THAN (95000),
 PARTITION `p16` VALUES LESS THAN (105000),
 PARTITION `p17` VALUES LESS THAN (115000),
 PARTITION `p18` VALUES LESS THAN (125000),
 PARTITION `pmax` VALUES LESS THAN (MAXVALUE));

set cte_max_recursion_depth = 1000000000;
insert into
    employees3 WITH RECURSIVE EmployeeGenerator AS (
        SELECT
            101 AS emp_id,
            'Emp00001' AS emp_name,
            FLOOR(RAND() * (150000 - 50000) + 50000) AS salary,
            FLOOR(RAND() * 3 + 1) AS dept_id
        UNION
        ALL
        SELECT
            emp_id + 1,
            CONCAT('Emp', LPAD(CAST(emp_id - 100 AS CHAR), 5, '0')),
            FLOOR(RAND() * (150000 - 50000) + 50000),
            FLOOR(RAND() * 3 + 1)
        FROM
            EmployeeGenerator
        WHERE
            emp_id < 20100
    )
SELECT
    *
FROM
    EmployeeGenerator;



analyze table employees3 partition p12;
show stats_histograms where table_name='employees3' and Column_name='PRIMARY'

2. What did you expect to see? (Required)

it should be not zero.

3. What did you see instead (Required)

4. What is your TiDB version? (Required)

[hawkingrei]

It has been fixed by #57269