To add to gonzalo's answer, both the *string literal* and the *field* need to *support unicode characters*.

### String Literal

Per Marc Gravell's answer on [What does N' stands for in a SQL script ?][2]:

> `'abcd'` is a literal for a <code>[var]char</code> string, occupying 4 bytes memory, and using *whatever code-page the SQL server is configured for*. 
> `N'abcd'` is a literal for a <code>n[var]char</code> string, occupying 8 bytes of memory, and using UTF-16. 

Where the `N` prefix stands for "*National*" Language in the SQL-92 standard and is used for representing unicode characters. For example, in the following code, any unicode characters in the basic string literal are first encoded into SQL Server's "code page":

[![`SELECT '≤' AS ['≤'], N'≤' AS [N'≤']`][1]][1]

> **Aside**: You can [check your code page][4] with the following SQL:
> 
 
> SELECT DATABASEPROPERTYEX('dbName', 'Collation') AS dbCollation;
 SELECT COLLATIONPROPERTY( 'SQL_Latin1_General_CP1_CI_AS' , 'CodePage' ) AS [CodePage];
> The default is [Windows-1252][3] which only [contains these 256 characters][5]

### Field Type

Once the values are capable of being *passed*, they'll also need to be capable of being *stored* into a [column that supports unicode types][8], for example:

* `nchar`
* `nvarchar`
* `ntext`

**Further Reading**:

* [Why do we need to put N before strings in Microsoft SQL Server?][6]
* [What is the meaning of the prefix N in T-SQL statements?][7]
* [You must precede all Unicode strings with a prefix N when you deal with Unicode string constants in SQL Server][9]
* [Why do some SQL strings have an 'N' prefix?][10]





[1]: https://i.stack.imgur.com/vmK7p.png
[2]: https://stackoverflow.com/a/14353311/1366033
[3]: https://en.wikipedia.org/wiki/Windows-1252 
[4]: https://stackoverflow.com/q/7321159/1366033
[5]: https://www.w3schools.com/charsets/ref_html_ansi.asp
[6]: https://softwareengineering.stackexchange.com/q/155859/87466
[7]: https://stackoverflow.com/q/10025032/1366033
[8]: https://learn.microsoft.com/en-us/sql/t-sql/data-types/nchar-and-nvarchar-transact-sql?view=sql-server-2017
[9]: https://web.archive.org/web/20150114081311/http://support.microsoft.com:80/kb/239530/en-us "ARCHIVE of http:&#47;&#47;support.microsoft.com/kb/239530/en-us"
[10]: https://web.archive.org/web/20150208024547/http://databases.aspfaq.com/general/why-do-some-sql-strings-have-an-n-prefix.html "ARCHIVE of http:&#47;&#47;databases.aspfaq.com/general/why-do-some-sql-strings-have-an-n-prefix.html"

I am trying to insert `≤` and `≥` into a symbol table where the column is of type `nvarchar`.

Is this possible or are these symbols not allowed in SQL Server?

