asl3 opened a new pull request, #47178:
URL: https://github.com/apache/spark/pull/47178
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### What changes were proposed in this pull request?
This PR is a follow-up to #47152 against `branch-3.5`.
Add migration guide for `CREATE TABLE AS SELECT...` behavior change.
SPARK-41859 changes the behaviour for `CREATE TABLE AS SELECT ...` from
OVERWRITE to APPEND when `spark.sql.legacy.allowNonEmptyLocationInCTAS` is set
to `true`:
```
drop table if exists test_table;
create table test_table location '/tmp/test_table' stored as parquet as
select 1 as col union all select 2 as col;
drop table if exists test_table;
create table test_table location '/tmp/test_table' stored as parquet as
select 3 as col union all select 4 as col;
select * from test_table;
```
This produces {3, 4} in Spark <3.4.0 and {1, 2, 3, 4} in Spark 3.4.0 and
later. This is a silent change in
`spark.sql.legacy.allowNonEmptyLocationInCTAS` behaviour which introduces wrong
results in the user application.
### Why are the changes needed?
This documents a behavior change starting in Spark 3.4 for `CREATE TABLE AS
SELECT`
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
`doc build
`
### Was this patch authored or co-authored using generative AI tooling?
No.
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