unexpected value caused by changing COUNT to COUNT(DISTINCT)

mysql> SELECT ige86.c6 AS col_1, COUNT( ige86.c2) AS col_2 FROM t1 AS ige86 GROUP BY ige86.c6;

+------------+-------+

| col_1      | col_2 |

+------------+-------+

| sample_3   |     1 |

| sample_4EH |     1 |

| sample_6   |     1 |

| sample_a   |     1 |

| sample_b   |     1 |

| sample_c   |     1 |

| sample_j   |     2 |

| sample_K   |     1 |

| sample_N   |     1 |

| sample_V   |     1 |

| sample_w   |     1 |

| sample_Xw9 |     1 |

| sample_z2  |     1 |

+------------+-------+

13 rows in set (0.00 sec)

mysql> SELECT ige86.c6 AS col_1, COUNT(DISTINCT ige86.c2) AS col_2 FROM t1 AS ige86 GROUP BY ige86.c6;

+------------+-------+

| col_1      | col_2 |

+------------+-------+

| sample_3   |     1 |

| sample_4EH |     1 |

| sample_6   |     1 |

| sample_a   |     1 |

| sample_b   |     1 |

| sample_c   |     1 |

| sample_J   |     2 |

| sample_K   |     1 |

| sample_N   |     1 |

| sample_V   |     1 |

| sample_w   |     1 |

| sample_Xw9 |     1 |

| sample_z2  |     1 |

+------------+-------+

13 rows in set (0.00 sec)

DROP DATABASE IF EXISTS test;

CREATE DATABASE IF NOT EXISTS test;

USE test;

CREATE TABLE t1 (

    c1 INT NOT NULL AUTO_INCREMENT,

    c2 VARCHAR(255) NOT NULL,

    c3 VARCHAR(255) NULL,

    c4 INT NULL,

    c5 DATE NOT NULL,

    c6 VARCHAR(10) NOT NULL,

    PRIMARY KEY (c1)

);

INSERT INTO t1 (c1, c2, c3, c4, c5, c6) VALUES (869, 'sample_c7p1upvgURcypCq2qQjLyGsvORugzxayb', 'sample_d', 61, '2025-03-01', 'sample_V');

INSERT INTO t1 (c1, c2, c3, c4, c5, c6) VALUES (5896, 'sample_svbavNTPjppeAtOYta7i2hXCn3W8cZxPDAxmPakzDxL0RuVwUrncuJn7R5boTlc1NwuijwjnlUPrGPsZc27oOAbkWFQUDIeAZLsoncJneCS', 'sample_0aZiwgdEOefWE8fT0bOOBYbiZe1ygCGIX0RCg13siYiBBin46BaZO915LDZmUFGNMRiNj7Gyxe2N09XIHZXgZ82Zvrfwl4UwJiHSYe7Yu2D4yhiYv8h985aU8NBUF', 81, '2025-06-30', 'sample_Xw9');

INSERT INTO t1 (c1, c2, c3, c4, c5, c6) VALUES (1321, 'sample_GzuK8ep3PBXtmQJHaPO9kHQUI4Wxs0Dc0IBC6YcdX3yw4abaji', 'sample_82W70GCz', 37, '2024-11-07', 'sample_c');

INSERT INTO t1 (c1, c2, c3, c4, c5, c6) VALUES (4810, 'sample_WTr08DCqYCuyJKWS6zeldXSmRC8bYfMyigG7FbEhwWCuc4e9FB0whtnHfn6Ux1AdxV6z9FxdHyjgPixTYjO1UCMlCT3xsJGfpbSkQFqPz9J9CBSLm3fc', 'sample_CPeihaQarEgTuTaBwrt9t1og4jtiqaTU5l68ez00bG04E580NezFJDFCDgGYCD49mLJycdt5ZguOtdYYgfGpok1cA2V0hyJUbYf4Sqdk3caqc11Mab9acvRwhdfiGzv6qWvGQMHhXUC1pSiz0ysBlQUnjgy1CHlv17ed087VNRnAvRko7uT1mimTrel', 98, '2025-02-22', 'sample_N');

INSERT INTO t1 (c1, c2, c3, c4, c5, c6) VALUES (4843, 'sample_8pnFA06WrGcBFGtPB69dc3ZJEzs1bbvslyJ5Px0hjisxRKspAMDgJq8pENTgPfQraQXsbsewcN2bi9BHVVfUA5ykNl3uG7yCJWEwb5qMyaNSksYthjlRVp9JulR74rNXDgbMmw9alXTvm', 'sample_Fg6CRQC67MFUqCzYOJAAIZF52PiUHqmuAyTFWxo06ew7FBqKZJ1Wk4ip4mNUNw8RDXU1aX5LXIYrz0I98kCebipnY4QG3TaPXNB6pObol984z7ioupPWJNMJCTp59lwr1LsK7p0UirM6jdtiAiaFusdzH82cKmnFkiMSItZbCZpIyjbFt6163R', 35, '2024-12-11', 'sample_j');

INSERT INTO t1 (c1, c2, c3, c4, c5, c6) VALUES (7723, 'sample_63nIxm66JybL6rB3h9VfsZ51qrwxNSQXiYKvVTWerCiRH6pO60GKQGqvIY8zE4QxEqgtE6stLBfMkatGzoyUpn3LPpIesKiGL6hFqS', 'sample_kSd3iUW35Vzv2sVBJa9COllNjXRxWHlfq9HT5bCTdQy75CKzZy5IuynMz18MdvfeHEEuglnsaGpSqVnNclYHgbOccG21DII63SsBWregNHG0mQ3bgi4affqngMNrxy59wPp3PeQEx0btshaB9J8OZ1glkI9ySKimC0mWWldGXsEqbeqp3093KU0zpccUTBaPKhC2jX4kwOyqv3W3NUhDWSZ', 100, '2024-11-11', 'sample_w');

INSERT INTO t1 (c1, c2, c3, c4, c5, c6) VALUES (4909, 'sample_FTqylLuaYkFrOqh8sOiScyzrv7X1ZeGypxEloQK2zCUro2q4Fn8htfYG4SioeP3MJKYu008JCVY2z0y8rYOMP8wFv5mNDPGq7sCajRVrZ8JUGQ9bCqRkdFyt4Uf6KSJ576MXGs7fu9', 'sample_6sQhejQPAIURyc6Ng7CwqIZAm5wrNbaiS3vidwmAsNYLMGhNjfYHHGiMdjxBPdnXawvp5RYvbOIkxmoOBmY069aPUg4jk3qJNOEmr0LvwuJ0xFIgRaxlxL3DulMYRhBMNr642jV9SiB0AHotGmOrtWEwaVinkFIz3mk', 96, '2025-06-22', 'sample_6');

INSERT INTO t1 (c1, c2, c3, c4, c5, c6) VALUES (7595, 'sample_DA0ksiV5EpFHmICoVQlDRbxcKYGGXg2fq0V0gvW4Wz29nQ', 'sample_a09LSrnICeqfvCXoQt4sCmyvVipFsWxTSLeyZgOGbBD2YyhBzzx2ZMavDCrXB9zl0jckOQFtwkZ8MIxRo5IXFnD9Kjx3fVVH3CoZoAEcT7WdqIWbz7piuFuBRatPhS9ux6ACeSZ0zkxmkm55GuRMmtutMEpnrMq2jr7bjkRKrJGG4bF1v38oWrtJDjfrSCsV7o47UPxJR26yYwXPcYha8HaU5AKMYVn4iqqQ2uWm7', 55, '2025-08-12', 'sample_J');

INSERT INTO t1 (c1, c2, c3, c4, c5, c6) VALUES (1263, 'sample_LtSMmcHVQaIPeYlEgZdz5evJHfVsvIVu3RfZqxuKhk8zOClUJqvz7mPIphyXY746ppo02SQXOZbJIHvckcANS8nRydxgZqndzfKnfHsIGqVoNapx9cLQAhJbdvnkn8KJlGd7F12dYmDlNxDu2KSyt6oBrVKgGXrrCI75O60hqDZNbX7xkyY7H3waSTrMlRm8JY4jF1ESKl8', 'sample_JlRV74SLN5FzROZNmdzdDGQRArjI4QnRWlHWBRWDyVxf05ti9BxvAKSP0H58x0gKJmCQAgJRfJSoxNphLRfkbmyNPk0pwVyJvTRcPQpsTe2t7o0fsNCyC6bj45dohsWJO7yDmM4iqbkxZcEW3ppTgjw83OH2RitNN0iVI6WI6HRxhNKq9whtZj5QJoTQ2I6ipoQW943a1Jzv3USe4pd68X3VYjohvFB7IZrU79k4Tfe', 65, '2025-08-10', 'sample_K');

INSERT INTO t1 (c1, c2, c3, c4, c5, c6) VALUES (6539, 'sample_j9zv7nWoe13BwI0Ob1fl7A7fuvAut3bwaPIJy7werfD5puh5mv6PPHV2sbN82LQjAKYgKjpxW3PT5OHEDFi1HyC', 'sample_U', 54, '2025-05-07', 'sample_3');

INSERT INTO t1 (c1, c2, c3, c4, c5, c6) VALUES (7575, 'sample_bEsnSzY3ivV3LHBrf8EpYBpWn1DAf2Eotl5AvmDbgDH', 'sample_2jKfszHoUB9DG3rRC4sQQEtl5Wtl7YrBrPPn53ovAz8xQp04r4UF47gbtSIBRDeZqsXSke8d9sy14bKt0uwoBRLAduo6tGEOPw4D0Ap5qk3TJqdg7DacyFVO', 95, '2024-12-27', 'sample_a');

INSERT INTO t1 (c1, c2, c3, c4, c5, c6) VALUES (1592, 'sample_qSPjIQ8cKvwtvLziXQcJFoesNKEZob8e2hoNrjd1uPADX0qXeLkvNh9Vg9VqrZXvAUGSfIy7vSre3DbktsHJE1po8zrtVJm5Abr3KxnNQa', 'sample_yOmvdklcbJ07kFTczB0SGp5yqq5opSwy3OX9TNCQUBlPhq6tLDXLXn1nh9hbvFA97zfLaW31VMkYy2b', 85, '2024-12-30', 'sample_b');

INSERT INTO t1 (c1, c2, c3, c4, c5, c6) VALUES (4154, 'sample_hhpe0EBx5uKO1uAlFYcBhGPXIqDx1via8q958w68ZHer86yuHubURN60nC2Y95EXelLgvMzsU1Rb7TkxRk7KxxpHUFsOSpGXMAdioCrPzwSFM7MLn9aaFDGKyrVqo7h7PoVKlBqSJJRDwnTyVpb4vM1FjtB4s5jwVQ7Jtjh', 'sample_ABR4RdoheahMSHnqNm3b081Z3Zzcop1cFfNbXiNjIWzNwKnscuRBvEzGiSYC7vypfh6gyhsGD1', 72, '2025-08-14', 'sample_z2');

INSERT INTO t1 (c1, c2, c3, c4, c5, c6) VALUES (1629, 'sample_1yTm01qWFQ1v6hKHQXCXcB1AY04EuyMSM4jykcvA4J7CsZeBVMDsi0dlFCTyGeT6BMEiTk6awWWrLAY88LhmJtthbb', 'sample_4FYd0rHTCF88gDoNC6dS4eYgQipiSHlfc2TBg6PbSheDphz5lQGExmrLnYRGgXSN3hldSPcHzyHX19YVYj46udQfl5nNHLkVx6rWXPxNGe2WfaaWT4Lptt09UendCgydCiNqapXRn385dOL0S3Nauf2XFNowygtEX6wNeIVH3Yp0HvJDJRQVKFfWBR5i2I00F6RlNfMeaDC', 11, '2025-03-01', 'sample_4EH');

SELECT ige86.c6 AS col_1, COUNT( ige86.c2) AS col_2 FROM t1 AS ige86 GROUP BY ige86.c6;

SELECT ige86.c6 AS col_1, COUNT(DISTINCT ige86.c2) AS col_2 FROM t1 AS ige86 GROUP BY ige86.c6;