SQL Server – Difference Between AND and &

COUNT(*) Returns all rows ignoring nulls right?

I'm not sure what you mean by "ignoring nulls" here. It returns the number of rows irrespective of any NULLs

SELECT COUNT(*)       
FROM (VALUES (CAST(NULL AS INT)),
             (CAST(NULL AS INT))) V(C)

Returns 2.

Altering the above query to COUNT(C) would return 0 as when using COUNT with an expression other than * only NOT NULL values of that expression are counted.

Suppose the table in your question has the following source data

+---------+---------------+
|  Name   | MaritalStatus |
+---------+---------------+
| Albert  | Single        |
| Bob     | Single        |
| Charles | Single        |
| David   | Single        |
| Edward  | Married       |
| Fred    | Married       |
| George  | NULL          |
+---------+---------------+

The query

SELECT MaritalStatus,
       COUNT(*) AS CountResult
FROM   T
GROUP  BY MaritalStatus 

Returns

+---------------+-------------+
| MaritalStatus | CountResult |
+---------------+-------------+
| Single        |           4 |
| Married       |           2 |
| NULL          |           1 |
+---------------+-------------+

Hopefully it is obvious how that result relates to the original data.

What does COUNT(*) OVER() do?

Adding that into the SELECT list for the previous query produces

+---------------+-------------+-----------------+
| MaritalStatus | CountResult | CountOverResult |
+---------------+-------------+-----------------+
| Single        |           4 |               3 |
| Married       |           2 |               3 |
| NULL          |           1 |               3 |
+---------------+-------------+-----------------+

Notice that the result set has 3 rows and CountOverResult is 3. This is not a coincidence.

The reason for this is because it logically operates on the result set after the GROUP BY.

COUNT(*) OVER () is a windowed aggregate. The absence of any PARTITION BY or ORDER BY clause means that the window it operates on is the whole result set.

In the case of the query in your question the value of CountOverResult is the same as the number of distinct MaritalStatus values that exist in the base table because there is one row for each of these in the grouped result.

You're trying to use a variable in places where you can't - as a part of the name of a trigger, and as the name of a table. Instead of passing @triggertable in as a parameter, you may as well just concatenate it directly into the SQL statement, replacing:

@triggertable

with:

' + @triggertable + '

Then, you should get the results you want. Given that you're getting the table names from system tables, you shouldn't actually have to worry about SQL injection here. Do double-check how the cursor returns the table name - in some cases, it may return:

[tablename]

instead of just:

tablename

As noted by Kenneth Fisher, try printing @sql instead of executing it to confirm it looks like what you want (since we've eliminated the parameters you were passing into sp_executesql).