LIKE operator as a replacement for RegEx - sql

Question

My task is to select entries for the following mask - SNNN000
Where:
"N" – any numerical symbol;
"S" – any numerical or alphabetic symbol(Latin);
"0" - any numerical or alphabetic symbol (Latin), can be
missed;
Here's what I got - "[0-9A-Za-z][0-9][0-9][0-9][0-9A-Za-z][0-9A-Za-z][0-9A-Za-z]".
There was a problem with "0", how can I make it so that the mask can ignore the conditions for this symbol? All entries except the 5th(Id) from the #table table should be displayed.
DECLARE #table TABLE (
id INT
,Txt NVARCHAR(100)
);
INSERT INTO #table (id, Txt)
VALUES (1, N'S123AB1')
,(2, N'S123')
,(3, N'S123A')
,(4, N'S123AB')
,(5, N'S123.#!');
SELECT *
FROM #table AS t
WHERE t.Txt LIKE N'[0-9A-Za-z][0-9][0-9][0-9][0-9A-Za-z][0-9A-Za-z][0-9A-Za-z]'
I understand that I could add conditions via the OR operator. But I would like to do it in a single expression and I could do it in regular expressions "[0-9A-Za-z]\d{3}[0-9A-Za-z]?[0-9A-Za-z]?[0-9A-Za-z]?". As I understand it, there are no full regular expressions in SQL, if I am wrong, then I would appreciate an explanation.
SELECT *
FROM #table AS t
WHERE t.Txt LIKE N'[0-9A-Za-z][0-9][0-9][0-9][0-9A-Za-z][0-9A-Za-z][0-9A-Za-z]'
OR t.Txt LIKE N'[0-9A-Za-z][0-9][0-9][0-9]';

Answer 1

Unfortunately, using OR is probably the best you can do using SQL Server's enhanced LIKE operator:
SELECT *
FROM #table AS t
WHERE
t.Txt LIKE N'[0-9A-Za-z][0-9][0-9][0-9]' OR
t.Txt LIKE N'[0-9A-Za-z][0-9][0-9][0-9][0-9A-Za-z]' OR
t.Txt LIKE N'[0-9A-Za-z][0-9][0-9][0-9][0-9A-Za-z][0-9A-Za-z]' OR
t.Txt LIKE N'[0-9A-Za-z][0-9][0-9][0-9][0-9A-Za-z][0-9A-Za-z][0-9A-Za-z]';

Answer 2

The simplest method I can think of is:
SELECT t.*
FROM #table AS t
WHERE (t.Txt + 'AAA') LIKE '[0-9A-Za-z][0-9][0-9][0-9][0-9A-Za-z][0-9A-Za-z][0-9A-Za-z]%' AND
LEN(t.Txt) BETWEEN 4 AND 7;
This adds three extra characters and checks that the first 7 characters match. It then validates the length of the column.