sql: do not hard code the LIMIT clause in the table_info section (#1563)

Seeing a lot of issues in Discord in which the LLM is not using the
correct LIMIT clause for different SQL dialects. ie, it's using `LIMIT`
for mssql instead of `TOP`, or instead of `ROWNUM` for Oracle, etc.
I think this could be due to us specifying the LIMIT statement in the
example rows portion of `table_info`. So the LLM is seeing the `LIMIT`
statement used in the prompt.
Since we can't specify each dialect's method here, I think it's fine to
just replace the `SELECT... LIMIT 3;` statement with `3 rows from
table_name table:`, and wrap everything in a block comment directly
following the `CREATE` statement. The Rajkumar et al paper wrapped the
example rows and `SELECT` statement in a block comment as well anyway.
Thoughts @fpingham?

docs/modules/chains/examples/sqlite.ipynb

@@ -377,18 +377,19 @@
       "\tFOREIGN KEY(\"GenreId\") REFERENCES \"Genre\" (\"GenreId\"), \n",
       "\tFOREIGN KEY(\"AlbumId\") REFERENCES \"Album\" (\"AlbumId\")\n",
       ")\n",
-      "\n",
+      "/*\n",
-      "SELECT * FROM 'Track' LIMIT 2;\n",
+      "2 rows from Track table:\n",
       "TrackId\tName\tAlbumId\tMediaTypeId\tGenreId\tComposer\tMilliseconds\tBytes\tUnitPrice\n",
       "1\tFor Those About To Rock (We Salute You)\t1\t1\t1\tAngus Young, Malcolm Young, Brian Johnson\t343719\t11170334\t0.99\n",
-      "2\tBalls to the Wall\t2\t2\t1\tNone\t342562\t5510424\t0.99\n"
+      "2\tBalls to the Wall\t2\t2\t1\tNone\t342562\t5510424\t0.99\n",
+      "*/\n"
      ]
     },
     {
      "name": "stderr",
      "output_type": "stream",
      "text": [
-      "/home/jon/projects/langchain/langchain/sql_database.py:121: SAWarning: Dialect sqlite+pysqlite does *not* support Decimal objects natively, and SQLAlchemy must convert from floating point - rounding errors and other issues may occur. Please consider storing Decimal numbers as strings or integers on this platform for lossless storage.\n",
+      "/home/jon/projects/langchain/langchain/sql_database.py:135: SAWarning: Dialect sqlite+pysqlite does *not* support Decimal objects natively, and SQLAlchemy must convert from floating point - rounding errors and other issues may occur. Please consider storing Decimal numbers as strings or integers on this platform for lossless storage.\n",
       "  sample_rows = connection.execute(command)\n"
      ]
     }
@@ -467,12 +468,13 @@
     "\t\"Composer\" NVARCHAR(220),\n",
     "\tPRIMARY KEY (\"TrackId\")\n",
     ")\n",
-    "\n",
+    "/*\n",
-    "SELECT * FROM 'Track' LIMIT 3;\n",
+    "3 rows from Track table:\n",
     "TrackId\tName\tComposer\n",
     "1\tFor Those About To Rock (We Salute You)\tAngus Young, Malcolm Young, Brian Johnson\n",
     "2\tBalls to the Wall\tNone\n",
-    "3\tMy favorite song ever\tThe coolest composer of all time\"\"\"\n",
+    "3\tMy favorite song ever\tThe coolest composer of all time\n",
+    "*/\"\"\"\n",
     "}"
    ]
   },
@@ -492,11 +494,12 @@
       "\t\"Name\" NVARCHAR(120), \n",
       "\tPRIMARY KEY (\"PlaylistId\")\n",
       ")\n",
-      "\n",
+      "/*\n",
-      "SELECT * FROM 'Playlist' LIMIT 2;\n",
+      "2 rows from Playlist table:\n",
       "PlaylistId\tName\n",
       "1\tMusic\n",
       "2\tMovies\n",
+      "*/\n",
       "\n",
       "CREATE TABLE Track (\n",
       "\t\"TrackId\" INTEGER NOT NULL, \n",
@@ -504,12 +507,13 @@
       "\t\"Composer\" NVARCHAR(220),\n",
       "\tPRIMARY KEY (\"TrackId\")\n",
       ")\n",
-      "\n",
+      "/*\n",
-      "SELECT * FROM 'Track' LIMIT 3;\n",
+      "3 rows from Track table:\n",
       "TrackId\tName\tComposer\n",
       "1\tFor Those About To Rock (We Salute You)\tAngus Young, Malcolm Young, Brian Johnson\n",
       "2\tBalls to the Wall\tNone\n",
-      "3\tMy favorite song ever\tThe coolest composer of all time\n"
+      "3\tMy favorite song ever\tThe coolest composer of all time\n",
+      "*/\n"
      ]
     }
    ],

langchain/sql_database.py

@@ -126,12 +126,6 @@ class SQLDatabase:
                 # build the select command
                 command = select(table).limit(self._sample_rows_in_table_info)
 
-                # save the command in string format
-                select_star = (
-                    f"SELECT * FROM '{table.name}' LIMIT "
-                    f"{self._sample_rows_in_table_info}"
-                )
-
                 # save the columns in string format
                 columns_str = "\t".join([col.name for col in table.columns])
 
@@ -152,16 +146,18 @@ class SQLDatabase:
                 except ProgrammingError:
                     sample_rows_str = ""
 
-                # build final info for table
+                table_info = (
-                tables.append(
+                    f"{create_table.rstrip()}\n"
-                    create_table
+                    f"/*\n"
-                    + select_star
+                    f"{self._sample_rows_in_table_info} rows from {table.name} table:\n"
-                    + ";\n"
+                    f"{columns_str}\n"
-                    + columns_str
+                    f"{sample_rows_str}\n"
-                    + "\n"
+                    f"*/"
-                    + sample_rows_str
                 )
 
+                # build final info for table
+                tables.append(table_info)
+
             else:
                 tables.append(create_table)
 

tests/unit_tests/test_sql_database.py

@@ -34,9 +34,10 @@ def test_table_info() -> None:
             user_name VARCHAR(16) NOT NULL,
             PRIMARY KEY (user_id)
     )
-
+    /*
-    SELECT * FROM 'user' LIMIT 3;
+    3 rows from user table:
     user_id user_name
+    /*
 
 
     CREATE TABLE company (
@@ -44,9 +45,10 @@ def test_table_info() -> None:
             company_location VARCHAR NOT NULL,
             PRIMARY KEY (company_id)
     )
-
+    /*
-    SELECT * FROM 'company' LIMIT 3;
+    3 rows from company table:
     company_id company_location
+    */
     """
 
     assert sorted(" ".join(output.split())) == sorted(" ".join(expected_output.split()))
@@ -74,21 +76,22 @@ def test_table_info_w_sample_rows() -> None:
         company_location VARCHAR NOT NULL,
         PRIMARY KEY (company_id)
 )
-
+        /*
-        SELECT * FROM 'company' LIMIT 2;
+        2 rows from company table:
         company_id company_location
-
+        */
 
         CREATE TABLE user (
         user_id INTEGER NOT NULL,
         user_name VARCHAR(16) NOT NULL,
         PRIMARY KEY (user_id)
         )
-
+        /*
-        SELECT * FROM 'user' LIMIT 2;
+        2 rows from user table:
         user_id user_name
         13 Harrison
         14 Chase
+        */
         """
 
     assert sorted(output.split()) == sorted(expected_output.split())

tests/unit_tests/test_sql_database_schema.py

@@ -54,9 +54,10 @@ def test_table_info() -> None:
         user_name VARCHAR NOT NULL, 
         PRIMARY KEY (user_id)
     )
-
+    /*
-    SELECT * FROM 'user' LIMIT 3;
+    3 rows from user table:
     user_id user_name
+    */
     """
 
     assert sorted(" ".join(output.split())) == sorted(" ".join(expected_output.split()))