SQL Server 2019 (Linux)

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

SELECT @@VERSION;


(No column name)


Microsoft SQL Server 2019 (RTM-CU18) (KB5017593) - 15.0.4261.1 (X64) 
	Sep 12 2022 15:07:06 
	Copyright (C) 2019 Microsoft Corporation
	Express Edition (64-bit) on Linux (Rocky Linux 8.6 (Green Obsidian)) <X64>


DROP TABLE IF EXISTS Fechas;

CREATE TABLE Fechas (
  DatoInicial NVARCHAR(7),
  DatoEsperado DATETIME
);

INSERT INTO Fechas
  (DatoInicial)
VALUES
  ('2022-01'),
  ('2022-02'),
  ('2022-03'),
  (NULL),
  ('2022-04'),
  ('2022-05')

SELECT
  DatoInicial,
  DatoEsperado
FROM
  Fechas

GO


DatoInicial
DatoEsperado


2022-01
null

2022-02
null

2022-03
null

null
null

2022-04
null

2022-05
null


ALTER TABLE
  Fechas
ALTER COLUMN
  DatoInicial NVARCHAR(10)

UPDATE
  Fechas
SET
  DatoInicial = EOMONTH(DatoInicial + '-01'),
  DatoEsperado = EOMONTH(DatoInicial + '-01')

SELECT
  DatoInicial,
  DatoEsperado
FROM
  Fechas

GO


DatoInicial
DatoEsperado


2022-01-31
2022-01-31 00:00:00.000

2022-02-28
2022-02-28 00:00:00.000

2022-03-31
2022-03-31 00:00:00.000

null
null

2022-04-30
2022-04-30 00:00:00.000

2022-05-31
2022-05-31 00:00:00.000


ALTER TABLE
  Fechas
ALTER COLUMN
  DatoInicial DATETIME

ALTER TABLE
  Fechas
DROP COLUMN
  DatoEsperado

SELECT
  DatoInicial
FROM
  Fechas

GO


DatoInicial


2022-01-31 00:00:00.000

2022-02-28 00:00:00.000

2022-03-31 00:00:00.000

null

2022-04-30 00:00:00.000

2022-05-31 00:00:00.000

DatoInicial	DatoEsperado
2022-01	null
2022-02	null
2022-03	null
null	null
2022-04	null
2022-05	null

DatoInicial	DatoEsperado
2022-01-31	2022-01-31 00:00:00.000
2022-02-28	2022-02-28 00:00:00.000
2022-03-31	2022-03-31 00:00:00.000
null	null
2022-04-30	2022-04-30 00:00:00.000
2022-05-31	2022-05-31 00:00:00.000