SQL Server 2022

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with cte as (
  select *
  from (
    values
    (123456, 3456, '31/03/2021', 0, null, 123, 456, 321, cast(null as int), cast(null as int), cast(null as int), 900)
    , (123456, 3456, '31/03/2021', 162.23, 1234, null, null, null, null, null, null, 1234)
    , (123456, 3456, '31/03/2021', 12.25, null, null, null, null, null, 240, null, 240)
    , (123456, 3456, '31/03/2021', 10, null, null, null, null, 120, null, null, 120)
  ) x (Employee_ID, PSNO, PSDATE, HOURS, BASIC, HRA, SHIFT, CHILD, OT1, OT2, OT3, GROSS)
)
select Employee_ID, PSNO, PSDATE
  , isnull(max(BASIC), 0) BASIC
  , max(case when BASIC is not null then HOURS else 0 end) BASIC_HRS
  , max(HRA) HRA
  , max(SHIFT) SHIFT
  , max(CHILD) CHILD
  , isnull(max(OT1), 0) OT1
  , max(case when OT1 is not null then HOURS else 0 end) OT1_HRS
  , isnull(max(OT2), 0) OT2
  , max(case when OT2 is not null then HOURS else 0 end) OT2_HRS
  , isnull(max(OT3), 0) OT3
  , max(case when OT3 is not null then HOURS else 0 end) OT3_HRS
  , sum(GROSS) GROSS
from cte
group by Employee_ID, PSNO, PSDATE;

Employee_ID	PSNO	PSDATE	BASIC	BASIC_HRS	HRA	SHIFT	CHILD	OT1	OT1_HRS	OT2	OT2_HRS	OT3	OT3_HRS	GROSS
123456	3456	31/03/2021	1234	162.23	123	456	321	120	10.00	240	12.25	0	0.00	2494

Warning: Null value is eliminated by an aggregate or other SET operation.