SQL Query Prompt update + added _execute method for SQLDatabase (#8100)

- Description: This pull request (PR) includes two minor changes:

1. Updated the default prompt for SQL Query Checker: The current prompt
does not clearly specify the final response that the LLM (Language
Model) should provide when checking for the query if `use_query_checker`
is enabled in SQLDatabase Chain. As a result, the LLM adds extra words
like "Here is your updated query" to the response. However, this causes
a syntax error when executing the SQL command in SQLDatabaseChain, as
these additional words are also included in the SQL query.

2. Moved the query's execution part into a separate method for
SQLDatabase: The purpose of this change is to provide users with more
flexibility when obtaining the result of an SQL query in the original
form returned by sqlalchemy. In the previous implementation, the run
method returned the results as a string. By creating a distinct method
for execution, users can now receive the results in original format,
which proves helpful in various scenarios. For example, during the
development of a tool, I found it advantageous to obtain results in
original format rather than a string, as currently done by the run
method.

- Tag maintainer: @hinthornw

---------

Co-authored-by: Bagatur <baskaryan@gmail.com>

libs/langchain/langchain/tools/sql_database/prompt.py

@@ -11,4 +11,8 @@ Double check the {dialect} query above for common mistakes, including:
 - Casting to the correct data type
 - Using the proper columns for joins
 
-If there are any of the above mistakes, rewrite the query. If there are no mistakes, just reproduce the original query."""
+If there are any of the above mistakes, rewrite the query. If there are no mistakes, just reproduce the original query.
+
+Output the final SQL query only.
+
+SQL Query: """

libs/langchain/langchain/utilities/sql_database.py

@@ -2,7 +2,7 @@
 from __future__ import annotations
 
 import warnings
-from typing import Any, Iterable, List, Optional
+from typing import Any, Iterable, List, Optional, Sequence
 
 import sqlalchemy
 from sqlalchemy import MetaData, Table, create_engine, inspect, select, text
@@ -368,12 +368,11 @@ class SQLDatabase:
             f"{sample_rows_str}"
         )
 
-    def run(self, command: str, fetch: str = "all") -> str:
-        """Execute a SQL command and return a string representing the results.
-
-        If the statement returns rows, a string of the results is returned.
-        If the statement returns no rows, an empty string is returned.
+    def _execute(self, command: str, fetch: Optional[str] = "all") -> Sequence:
+        """
+        Executes SQL command through underlying engine.
 
+        If the statement returns no rows, an empty list is returned.
         """
         with self._engine.begin() as connection:
             if self._schema is not None:
@@ -395,26 +394,30 @@ class SQLDatabase:
                     result = cursor.fetchone()  # type: ignore
                 else:
                     raise ValueError("Fetch parameter must be either 'one' or 'all'")
+                return result
+        return []
 
-                # Convert columns values to string to avoid issues with sqlalchmey
-                # trunacating text
-                if isinstance(result, list):
-                    return str(
-                        [
-                            tuple(
-                                truncate_word(c, length=self._max_string_length)
-                                for c in r
-                            )
-                            for r in result
-                        ]
-                    )
+    def run(self, command: str, fetch: str = "all") -> str:
+        """Execute a SQL command and return a string representing the results.
 
-                return str(
-                    tuple(
-                        truncate_word(c, length=self._max_string_length) for c in result
-                    )
-                )
-        return ""
+        If the statement returns rows, a string of the results is returned.
+        If the statement returns no rows, an empty string is returned.
+        """
+        result = self._execute(command, fetch)
+        # Convert columns values to string to avoid issues with sqlalchemy
+        # truncating text
+        if not result:
+            return ""
+        elif isinstance(result, list):
+            res: Sequence = [
+                tuple(truncate_word(c, length=self._max_string_length) for c in r)
+                for r in result
+            ]
+        else:
+            res = tuple(
+                truncate_word(c, length=self._max_string_length) for c in result
+            )
+        return str(res)
 
     def get_table_info_no_throw(self, table_names: Optional[List[str]] = None) -> str:
         """Get information about specified tables.