Postgres 14

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.
CREATE TABLE subject_master
    ("subject_id" varchar(13), "subject_name" varchar(9), "status" varchar(6))
;
    
INSERT INTO subject_master
    ("subject_id", "subject_name", "status")
VALUES
    ('UHGAwlfrGDFwU', 'Maths', 'active'),
    ('X3Sv7nE5HqhXg', 'Physics', 'active'),
    ('Y7fHY4mEJmHaS', 'Chemistry', 'active')
;
3 rows affected

CREATE TABLE slot_master
    ("slot_id" varchar(13), "subject_id" varchar(13), "date" varchar(10), "start_time" varchar(5))
;
    
INSERT INTO slot_master
    ("slot_id", "subject_id", "date", "start_time")
VALUES
    ('aMkJaKeTMSqRt', 'Y7fHY4mEJmHaS', '02-08-2022', '06:00'),
    ('Njpm1BJknxaHb', 'Y7fHY4mEJmHaS', '04-08-2022', '06:00'),
    ('XwE8fGvFp8ofI', 'Y7fHY4mEJmHaS', '06-08-2022', '06:00'),
    ('J0FnzWAcdNBIb', 'Y7fHY4mEJmHaS', '09-08-2022', '06:00'),
    ('7jKgQM9Ly7xB1', 'Y7fHY4mEJmHaS', '11-08-2022', '06:00'),
    ('LaQD4KMgrNfQp', 'Y7fHY4mEJmHaS', '13-08-2022', '06:00'),
    ('jOB2zXHhUvzUZ', 'Y7fHY4mEJmHaS', '16-08-2022', '06:00'),
    ('wQ8anzVi649H2', 'Y7fHY4mEJmHaS', '18-08-2022', '06:00'),
    ('8koqL52n1rNWX', 'Y7fHY4mEJmHaS', '20-08-2022', '06:00'),
    ('5HOMvEBusoSGO', 'X3Sv7nE5HqhXg', '01-08-2022', '09:00'),
    ('Nm437BpC2oOoW', 'X3Sv7nE5HqhXg', '03-08-2022', '09:00'),
    ('VOs9BTmA4j1ar', 'X3Sv7nE5HqhXg', '05-08-2022', '09:00'),
    ('1DCSINyTS80aD', 'X3Sv7nE5HqhXg', '08-08-2022', '09:00'),
    ('ihl0sv0RANvbs', 'X3Sv7nE5HqhXg', '10-08-2022', '09:00'),
    ('mbAg9pr9PopNW', 'X3Sv7nE5HqhXg', '12-08-2022', '09:00'),
    ('VUVJlWCbgo30h', 'X3Sv7nE5HqhXg', '15-08-2022', '09:00'),
    ('LAW8p1XTe2GzW', 'X3Sv7nE5HqhXg', '17-08-2022', '09:00'),
    ('l9JweYVRhrKiH', 'X3Sv7nE5HqhXg', '19-08-2022', '09:00'),
    ('4rhxtLpBIgk60', 'UHGAwlfrGDFwU', '13-08-2022', '06:00'),
    ('7PYANuy3cfI9b', 'UHGAwlfrGDFwU', '04-08-2022', '06:00'),
    ('ariHVdxwq9Qlq', 'UHGAwlfrGDFwU', '11-08-2022', '06:00'),
    ('eoabdysdnEhgo', 'UHGAwlfrGDFwU', '06-08-2022', '06:00'),
    ('l6CPBB8GHVdMz', 'UHGAwlfrGDFwU', '09-08-2022', '06:00'),
    ('nMzwARCSb4gun', 'UHGAwlfrGDFwU', '02-08-2022', '06:00'),
    ('RotO7tJeYGUks', 'UHGAwlfrGDFwU', '16-08-2022', '06:00'),
    ('UXaDInLqulUGp', 'UHGAwlfrGDFwU', '18-08-2022', '06:00')
;
26 rows affected

SELECT date( "date")   FROM slot_master


date


2022-08-02

2022-08-04

2022-08-06

2022-08-09

2022-08-11

2022-08-13

2022-08-16

2022-08-18

2022-08-20

2022-08-01

2022-08-03

2022-08-05

2022-08-08

2022-08-10

2022-08-12

2022-08-15

2022-08-17

2022-08-19

2022-08-13

2022-08-04

2022-08-11

2022-08-06

2022-08-09

2022-08-02

2022-08-16

2022-08-18


WITH CTE As (SELECT 
      "subject_id"
      , "date"
      , "start_time"
      , ROW_NUMBER() OVER(PARTITION BY "subject_id" ORDER BY  "date", "start_time") rn
FROM slot_master 
WHERE DATE("date") + "start_time"::time  > DATE('2022-07-3') + '05:00'::time)
SELECT       CTE."subject_id"
,subject_name
      , "date"
      , "start_time" FROM CTE  INNER JOIN  subject_master ON cTE.subject_id = subject_master.subject_id
WHERE subject_master.status = 'active' AND rn = 1


subject_id
subject_name
date
start_time


UHGAwlfrGDFwU
Maths
02-08-2022
06:00

X3Sv7nE5HqhXg
Physics
01-08-2022
09:00

Y7fHY4mEJmHaS
Chemistry
02-08-2022
06:00
subject_id	subject_name	date	start_time
UHGAwlfrGDFwU	Maths	02-08-2022	06:00
X3Sv7nE5HqhXg	Physics	01-08-2022	09:00
Y7fHY4mEJmHaS	Chemistry	02-08-2022	06:00