dongjoon-hyun commented on code in PR #60075:
URL: https://github.com/apache/spark/pull/60075#discussion_r4471098104


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docs/sql-migration-guide.md:
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@@ -74,6 +74,7 @@ license: |
 - Since Spark 4.4, `CREATE TABLE`, `REPLACE TABLE`, and `ALTER TABLE ... ADD 
CONSTRAINT` on a Data Source V2 table fail with 
`USER_DEFINED_FUNCTION_IN_CHECK_CONSTRAINT` when the condition of a CHECK 
constraint calls a user-defined scalar function, including a Data Source V2 
function. `ALTER TABLE ... ADD CONSTRAINT` keeps failing with 
`UNSUPPORTED_SQL_UDF_USAGE` on a SQL function. Previously, a write could 
resolve the function name in its own session, so that it enforced another rule 
or failed (SPARK-60777). To run these statements, change the condition to call 
only built-in functions. Existing constraints that call a user-defined function 
are not rejected.
 - Since Spark 4.4, `CREATE TABLE` and `REPLACE TABLE` on a Data Source V2 
table fail with `AGGREGATE_OR_WINDOW_FUNCTION_IN_CHECK_CONSTRAINT` when the 
condition of a CHECK constraint calls an aggregate or window function, 
including a user-defined aggregate function, `grouping`, and `grouping_id`. 
`ALTER TABLE ... ADD CONSTRAINT` keeps failing with its existing errors, such 
as `INVALID_WHERE_CONDITION` and `WINDOW_FUNCTION_NOT_ALLOWED_IN_CLAUSE`. 
Previously, these statements succeeded and every later write to the table 
failed (SPARK-60800). To run these statements, remove the function from the 
condition. Existing constraints that call these functions are not rejected.
 - Since Spark 4.4, `CREATE TABLE` and `REPLACE TABLE` on a Data Source V2 
table fail with `GENERATOR_IN_CHECK_CONSTRAINT` when the condition of a CHECK 
constraint calls a generator function, such as `explode`, `posexplode`, and 
`inline`. `ALTER TABLE ... ADD CONSTRAINT` keeps failing with 
`UNSUPPORTED_GENERATOR.OUTSIDE_SELECT`. Previously, these statements succeeded 
and every later write to the table failed (SPARK-60821). To run these 
statements, remove the function from the condition. Existing constraints that 
call a generator function are not rejected.
+- Since Spark 4.4, `CREATE TABLE` and `REPLACE TABLE` fail with 
`UNSUPPORTED_EXPRESSION_GENERATED_COLUMN` when the data type of a generation 
expression names its struct fields differently from the column type, in name, 
including letter case, or in order, for example `named_struct('y', a, 'x', b)`, 
`named_struct('X', b, 'Y', a)`, or `struct(a, b)` for a `STRUCT<x: INT, y: 
INT>` column. Previously, such an expression was accepted, although Spark lines 
up the struct fields by name, with the case sensitivity of the writing session, 
when it computes the value of a generated column of a Data Source V2 table, and 
by position when it checks a provided value (SPARK-60857). To line up the 
fields by position, cast the expression to the column type, for example 
`CAST(struct(a, b) AS STRUCT<x: INT, y: INT>)`. Existing tables with such an 
expression are not rejected, and a write that carries a row that Spark 
auto-filled into one of them keeps failing the check.

Review Comment:
   Thank you for checking each shape. You're right, the sentence holds only for 
fields of the same type in another order. I changed it in both the migration 
guide and the description to say that existing tables are not rejected and that 
this change does not affect writes to them. I used "does not affect" rather 
than "behave as before" since SPARK-60757 also changed the check of a provided 
value in 4.4.
   



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