maropu commented on a change in pull request #28953:
URL: https://github.com/apache/spark/pull/28953#discussion_r451339072
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File path: docs/sql-data-sources-jdbc.md
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@@ -156,6 +156,20 @@ the following case-insensitive options:
</td>
</tr>
+ <tr>
+ <td><code>preActions</code></td>
+ <td>
+ Custom queries which you want to run before reading data from JDBC or
writing data to JDBC. Only DDL or DML (insert/update/delete) are allowed. It is
called per DataFrame, not per session. You can specify multiple queries
separated by semicolon. When exceptions occur in preActions, the queries in
preActions will be rollbacked.
Review comment:
>> It is called per DataFrame, not per session.
I think this statement looks ambiguous. What does `per DataFrame` mean?
Probably, `per session` means `sessionInitStatement` though.
One more question; is there any usecase `preActions` can handle and
`sessionInitStatement` cannot?
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