[GitHub] [spark] RussellSpitzer commented on a diff in pull request #38823: [SPARK-41290][SQL] Support GENERATED ALWAYS AS expressions for columns in create/replace table statements

[GitBox <gi...@apache.org>]

RussellSpitzer commented on code in PR #38823:
URL: https://github.com/apache/spark/pull/38823#discussion_r1043702758


##########
sql/catalyst/src/main/java/org/apache/spark/sql/connector/catalog/TableProvider.java:
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@@ -93,4 +93,18 @@ default Transform[] inferPartitioning(CaseInsensitiveStringMap options) {
   default boolean supportsExternalMetadata() {
     return false;
   }
+
+  /**
+   * Returns true if the source supports defining generated columns upon table creation in SQL.
+   * When false: any create/replace table statements with a generated column defined in the table
+   * schema will throw an exception during analysis.
+   *
+   * A generated column is defined with syntax: {@code colName colType GENERATED ALWAYS AS (expr)}
+   * The generation expression is stored in the column metadata with key "generationExpression".
+   *
+   * Override this method to allow defining generated columns in create/replace table statements.
+   */
+  default boolean supportsGeneratedColumnsOnCreation() {

Review Comment:
   Sounds like it would need to be more like a CatalogCapability? Supports Creating Tables with Generated Columns? 
   
   Although in general i'm not sure how most other engines would be able to support this without supporting Spark Expressions. Do we have a limit on how much of the Spark API is included here?



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