feat: support to create external table (#1372)

* feat: support to create external table

* chore: apply suggestions from CR

* test: add create external table without ts type

* chore: apply suggestions from CR

* fix: fix import typo

* refactor: move consts to table crate

* chore: apply suggestions from CR

* refactor: rename create_table_schema

src/common/datasource/src/file_format.rs

@@ -26,13 +26,14 @@ use std::sync::Arc;
 use std::task::Poll;
 
 use arrow::record_batch::RecordBatch;
-use arrow_schema::{ArrowError, Schema};
+use arrow_schema::{ArrowError, Schema as ArrowSchema};
 use async_trait::async_trait;
 use bytes::{Buf, Bytes};
 use datafusion::error::{DataFusionError, Result as DataFusionResult};
 use datafusion::physical_plan::file_format::FileOpenFuture;
 use futures::StreamExt;
 use object_store::ObjectStore;
+use snafu::ResultExt;
 
 use self::csv::CsvFormat;
 use self::json::JsonFormat;
@@ -73,7 +74,7 @@ impl TryFrom<&HashMap<String, String>> for Format {
 
 #[async_trait]
 pub trait FileFormat: Send + Sync + std::fmt::Debug {
-    async fn infer_schema(&self, store: &ObjectStore, path: String) -> Result<Schema>;
+    async fn infer_schema(&self, store: &ObjectStore, path: String) -> Result<ArrowSchema>;
 }
 
 pub trait ArrowDecoder: Send + 'static {
@@ -154,3 +155,15 @@ pub fn open_with_decoder<T: ArrowDecoder, F: Fn() -> DataFusionResult<T>>(
         Ok(stream.boxed())
     }))
 }
+
+pub async fn infer_schemas(
+    store: &ObjectStore,
+    files: &[String],
+    file_format: &dyn FileFormat,
+) -> Result<ArrowSchema> {
+    let mut schemas = Vec::with_capacity(files.len());
+    for file in files {
+        schemas.push(file_format.infer_schema(store, file.to_string()).await?)
+    }
+    ArrowSchema::try_merge(schemas).context(error::MergeSchemaSnafu)
+}