SYBASE: Added offset support

Fixes: #5294

### Description
Fix for https://github.com/sqlalchemy/sqlalchemy/issues/5294#issue-610311455

I tested it against our database (Adaptive Server Enterprise/16.0 SP02) with `pyodbc+sybase`

### Checklist

This pull request is:

- [x] A short code fix for #5294
- [x] Added tests.

Closes: #5312
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/5312
Pull-request-sha: f62c14825f2941fdd54ede17fd8d4f105a052e05

Change-Id: Ic716e17a6f654deef78781cefc3f16333cd725c3

1 files changed, 8 insertions, 13 deletions

diff --git a/lib/sqlalchemy/dialects/sybase/base.py b/lib/sqlalchemy/dialects/sybase/base.py
index 77ebfac93..e3848a9b2 100644
--- a/lib/sqlalchemy/dialects/sybase/base.py
+++ b/lib/sqlalchemy/dialects/sybase/base.py
@@ -516,23 +516,18 @@ class SybaseSQLCompiler(compiler.SQLCompiler):
         {"doy": "dayofyear", "dow": "weekday", "milliseconds": "millisecond"},
     )
 
-    def get_select_precolumns(self, select, **kw):
-        s = select._distinct and "DISTINCT " or ""
-
-        if select._simple_int_limit and not select._offset:
-            kw["literal_execute"] = True
-            s += "TOP %s " % self.process(select._limit_clause, **kw)
-
-        if select._offset:
-            raise NotImplementedError("Sybase ASE does not support OFFSET")
-        return s
-
     def get_from_hint_text(self, table, text):
         return text
 
     def limit_clause(self, select, **kw):
-        # Limit in sybase is after the select keyword
-        return ""
+        text = ""
+        if select._limit_clause is not None:
+            text += " ROWS LIMIT " + self.process(select._limit_clause, **kw)
+        if select._offset_clause is not None:
+            if select._limit_clause is None:
+                text += " ROWS"
+            text += " OFFSET " + self.process(select._offset_clause, **kw)
+        return text
 
     def visit_extract(self, extract, **kw):
         field = self.extract_map.get(extract.field, extract.field)