Automatically create the tables for the SqlCatalog (#186)

* ensure tables exist on init

* make private

* remove unnecessary comment

* style

Author: cosmastech

mkdocs/docs/api.md

@@ -54,12 +54,6 @@ catalog = load_catalog(
 )
 ```
 
-If the catalog has not been initialized before, you need to run:
-
-```python
-catalog.create_tables()
-```
-
 Let's create a namespace:
 
 ```python

pyiceberg/catalog/sql.py

@@ -31,7 +31,7 @@
     union,
     update,
 )
-from sqlalchemy.exc import IntegrityError
+from sqlalchemy.exc import IntegrityError, OperationalError
 from sqlalchemy.orm import (
     DeclarativeBase,
     Mapped,
@@ -98,6 +98,18 @@ def __init__(self, name: str, **properties: str):
             raise NoSuchPropertyException("SQL connection URI is required")
         self.engine = create_engine(uri_prop, echo=True)
 
+        self._ensure_tables_exist()
+
+    def _ensure_tables_exist(self) -> None:
+        with Session(self.engine) as session:
+            for table in [IcebergTables, IcebergNamespaceProperties]:
+                stmt = select(1).select_from(table)
+                try:
+                    session.scalar(stmt)
+                except OperationalError:
+                    self.create_tables()
+                    return
+
     def create_tables(self) -> None:
         SqlCatalogBaseTable.metadata.create_all(self.engine)