refactor: route schema queries through adapter methods

- list_schemas() uses adapter.list_schemas_sql()
- make_classes() uses adapter.list_tables_sql() instead of SHOW TABLES
- Schema.exists uses new adapter.schema_exists_sql() method
- Added schema_exists_sql() to base, MySQL, and PostgreSQL adapters

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: dimitri-yatsenko

src/datajoint/adapters/base.py

@@ -615,6 +615,23 @@ def list_schemas_sql(self) -> str:
         """
         ...
 
+    @abstractmethod
+    def schema_exists_sql(self, schema_name: str) -> str:
+        """
+        Generate query to check if a schema exists.
+
+        Parameters
+        ----------
+        schema_name : str
+            Name of schema to check.
+
+        Returns
+        -------
+        str
+            SQL query that returns a row if the schema exists.
+        """
+        ...
+
     @abstractmethod
     def list_tables_sql(self, schema_name: str, pattern: str | None = None) -> str:
         """

src/datajoint/adapters/mysql.py

@@ -611,6 +611,10 @@ def list_schemas_sql(self) -> str:
         """Query to list all databases in MySQL."""
         return "SELECT schema_name FROM information_schema.schemata"
 
+    def schema_exists_sql(self, schema_name: str) -> str:
+        """Query to check if a database exists in MySQL."""
+        return f"SELECT schema_name FROM information_schema.schemata WHERE schema_name = {self.quote_string(schema_name)}"
+
     def list_tables_sql(self, schema_name: str, pattern: str | None = None) -> str:
         """Query to list tables in a database."""
         sql = f"SHOW TABLES IN {self.quote_identifier(schema_name)}"

src/datajoint/adapters/postgres.py

@@ -721,6 +721,10 @@ def list_schemas_sql(self) -> str:
             "WHERE schema_name NOT IN ('pg_catalog', 'information_schema')"
         )
 
+    def schema_exists_sql(self, schema_name: str) -> str:
+        """Query to check if a schema exists in PostgreSQL."""
+        return f"SELECT schema_name FROM information_schema.schemata WHERE schema_name = {self.quote_string(schema_name)}"
+
     def list_tables_sql(self, schema_name: str, pattern: str | None = None) -> str:
         """Query to list tables in a schema."""
         sql = (

src/datajoint/schemas.py

@@ -345,7 +345,7 @@ def make_classes(self, into: dict[str, Any] | None = None) -> None:
                 del frame
         tables = [
             row[0]
-            for row in self.connection.query("SHOW TABLES in `%s`" % self.database)
+            for row in self.connection.query(self.connection.adapter.list_tables_sql(self.database))
             if lookup_class_name("`{db}`.`{tab}`".format(db=self.database, tab=row[0]), into, 0) is None
         ]
         master_classes = (Lookup, Manual, Imported, Computed)
@@ -423,13 +423,7 @@ def exists(self) -> bool:
         """
         if self.database is None:
             raise DataJointError("Schema must be activated first.")
-        return bool(
-            self.connection.query(
-                "SELECT schema_name FROM information_schema.schemata WHERE schema_name = '{database}'".format(
-                    database=self.database
-                )
-            ).rowcount
-        )
+        return bool(self.connection.query(self.connection.adapter.schema_exists_sql(self.database)).rowcount)
 
     @property
     def lineage_table_exists(self) -> bool:
@@ -838,12 +832,8 @@ def list_schemas(connection: Connection | None = None) -> list[str]:
     list[str]
         Names of all accessible schemas.
     """
-    return [
-        r[0]
-        for r in (connection or _get_singleton_connection()).query(
-            'SELECT schema_name FROM information_schema.schemata WHERE schema_name <> "information_schema"'
-        )
-    ]
+    conn = connection or _get_singleton_connection()
+    return [r[0] for r in conn.query(conn.adapter.list_schemas_sql())]
 
 
 def virtual_schema(