fix loading of sql chain (#10860)

Closing #6889

libs/langchain/langchain/chains/loading.py

@@ -358,10 +358,16 @@ def _load_qa_with_sources_chain(config: dict, **kwargs: Any) -> QAWithSourcesCha
 
 
 def _load_sql_database_chain(config: dict, **kwargs: Any) -> Any:
+    from langchain_experimental.sql import SQLDatabaseChain
+
     if "database" in kwargs:
         database = kwargs.pop("database")
     else:
         raise ValueError("`database` must be present.")
+    if "llm_chain" in config:
+        llm_chain_config = config.pop("llm_chain")
+        chain = load_chain_from_config(llm_chain_config)
+        return SQLDatabaseChain(llm_chain=chain, database=database, **config)
     if "llm" in config:
         llm_config = config.pop("llm")
         llm = load_llm_from_config(llm_config)
@@ -374,7 +380,6 @@ def _load_sql_database_chain(config: dict, **kwargs: Any) -> Any:
         prompt = load_prompt_from_config(prompt_config)
     else:
         prompt = None
-    from langchain_experimental.sql import SQLDatabaseChain
 
     return SQLDatabaseChain.from_llm(llm, database, prompt=prompt, **config)