MySQL Bugs: #30215: Connector\J and MySQL command-line utility treat "---" (3-dashes) differently

Bug #30215	Connector\J and MySQL command-line utility treat "---" (3-dashes) differently
Submitted:	2 Aug 2007 22:45	Modified:	3 Oct 2007 16:56
Reporter:	Christopher Schultz	Email Updates:
Status:	Duplicate	Impact on me:	None
Category:	Connector / J	Severity:	S3 (Non-critical)
Version:	5.0.4	OS:	Any
Assigned to:		CPU Architecture:	Any

Description:
Issue this multi-line query using the MySQL command-line utility and you will get:

mysql> SELECT
    -> ---
    -> --- This is a comment
    -> ---
    -> 1 AS num
    -> ;
+-----+
| num |
+-----+
|   1 | 
+-----+
1 row in set (0.01 sec)

Issue the same multi-line query through Connector/J and the results will be different:

Running query:
SELECT
---
--- This is a comment
---
1 AS num
Results:
num
-1

(Please see the attached sample Java code to demonstrate).

The MySQL documentation seems to indicate that "--"-style comments must be followed by whitespace or a control character to avoid unfortunate bugs (http://dev.mysql.com/doc/refman/5.0/en/comments.html and http://dev.mysql.com/doc/refman/5.0/en/ansi-diff-comments.html). One particular comment in the documentation is very relevant:

  "Another safe feature is that the mysql  command-line client ignores lines that start with ‘--’."

So, the documentation states that "--" followed by a non-whitespace character (as is the case for "---") is required for comments, but then the command-line utility allows /any/ line that begins with "--" to be treated as a comment. I believe this is a discrepancy that needs to be corrected. It is very confusing to have a query behave one way through the MySQL client, and another way through the JDBC driver.

How to repeat:
Run this query using both MySQL command-line utility and through the Conenctor/J JDBC driver:

SELECT
---
--- This is a comment
---
1 AS num

Test file that demonstrates the behavior of the JDBC driver.

Attachment: CommentTest.java (application/octet-stream, text), 2.42 KiB.

Hi Christopher and thanks for another bug report.

Verified as described with test case attached:
 - MySQL 5.0.48 on WinXP Pro SP2
 - JDK 1.5.0_11 and latest c/J 5.0 sources

Apparently, the value of column "num" is -1...

.Loading JDBC driver 'com.mysql.jdbc.Driver'
Done.

Done.

Connected to 5.0.48-pb1030-log
F
Time: 2,266
There was 1 failure:
1) testbug30215(testsuite.simple.TestBug30215)junit.framework.ComparisonFailure: expected:<-...> but was:<...>

Test case on latest c/J 5.0 sources

Attachment: TestBug30215.java (text/x-java), 1.15 KiB.

Thanks for the quick turnaround on this bug. I'm not entirely sure what the resolution should be.

On the one hand, the MySQL command-line behavior is very nice in this particular case. On the other hand, the documentation makes a compelling case against treating all "--" as comment-until-newline indicators.

Someone also pointed out to me that even treating "\n--" as a comment-until-newline indicator might not work inside of a literal string. I'm not sure how sensitive the query parser is to string literals, but as long as those could be ignored, then I would vote for treating all non-literal "\n--" strings as comment-until-newline indicators.

Thanks!

Duplicate of Bug#26215.