[GitHub] [spark] maropu commented on a change in pull request #27909: [SPARK-31151][SQL][DOC] Reorganize the migration guide of SQL

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maropu commented on a change in pull request #27909: [SPARK-31151][SQL][DOC] Reorganize the migration guide of SQL
URL: https://github.com/apache/spark/pull/27909#discussion_r392561520
 
 

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 File path: docs/sql-migration-guide.md
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 @@ -26,92 +26,113 @@ license: |
   - Since Spark 3.1, grouping_id() returns long values. In Spark version 3.0 and earlier, this function returns int values. To restore the behavior before Spark 3.0, you can set `spark.sql.legacy.integerGroupingId` to `true`.
 
 ## Upgrading from Spark SQL 2.4 to 3.0
-  - Since Spark 3.0, when inserting a value into a table column with a different data type, the type coercion is performed as per ANSI SQL standard. Certain unreasonable type conversions such as converting `string` to `int` and `double` to `boolean` are disallowed. A runtime exception will be thrown if the value is out-of-range for the data type of the column. In Spark version 2.4 and earlier, type conversions during table insertion are allowed as long as they are valid `Cast`. When inserting an out-of-range value to a integral field, the low-order bits of the value is inserted(the same as Java/Scala numeric type casting). For example, if 257 is inserted to a field of byte type, the result is 1. The behavior is controlled by the option `spark.sql.storeAssignmentPolicy`, with a default value as "ANSI". Setting the option as "Legacy" restores the previous behavior.
-
-  - In Spark 3.0, the deprecated methods `SQLContext.createExternalTable` and `SparkSession.createExternalTable` have been removed in favor of its replacement, `createTable`.
-
-  - In Spark 3.0, the deprecated `HiveContext` class has been removed. Use `SparkSession.builder.enableHiveSupport()` instead.
-
-  - Since Spark 3.0, configuration `spark.sql.crossJoin.enabled` become internal configuration, and is true by default, so by default spark won't raise exception on sql with implicit cross join.
-
-  - In Spark version 2.4 and earlier, SQL queries such as `FROM <table>` or `FROM <table> UNION ALL FROM <table>` are supported by accident. In hive-style `FROM <table> SELECT <expr>`, the `SELECT` clause is not negligible. Neither Hive nor Presto support this syntax. Therefore we will treat these queries as invalid since Spark 3.0.
 
-  - Since Spark 3.0, the Dataset and DataFrame API `unionAll` is not deprecated any more. It is an alias for `union`.
+### DML
 
 Review comment:
   not DML but DDL?

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