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https://issues.apache.org/jira/browse/SPARK-17647?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15523623#comment-15523623
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Xiangrui Meng edited comment on SPARK-17647 at 9/26/16 5:07 PM:
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Thanks [~joshrosen]! I updated the JIRA description. The LIKE escaping
behaviors in MySQL/PostgreSQL are documented here:
* MySQL:
http://dev.mysql.com/doc/refman/5.7/en/string-comparison-functions.html#operator_like
* PostgreSQL: https://www.postgresql.org/docs/8.3/static/functions-matching.html
In particular, MySQL:
{noformat}
Exception: At the end of the pattern string, backslash can be specified as “\\”.
At the end of the string, backslash stands for itself because there is nothing
following to escape.
{noformat}
That explains why MySQL returns true for both
{code}
'\\' like '\\\\'
'\\' like '\\'
{code}
was (Author: mengxr):
Thanks [~joshrosen]! I updated the JIRA description. The LIKE escaping
behaviors in MySQL/PostgreSQL are documented here:
* MySQL:
http://dev.mysql.com/doc/refman/5.7/en/string-comparison-functions.html#operator_like
* PostgreSQL: https://www.postgresql.org/docs/8.3/static/functions-matching.html
In particular, MySQL:
{noformat}
Exception: At the end of the pattern string, backslash can be specified as “\\”.
At the end of the string, backslash stands for itself because there is nothing
following to escape.
{noformat}
That explains why MySQL returns true for both `\\` like `\\\\` and `\\` like
`\\`.
> SQL LIKE does not handle backslashes correctly
> ----------------------------------------------
>
> Key: SPARK-17647
> URL: https://issues.apache.org/jira/browse/SPARK-17647
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Reporter: Xiangrui Meng
> Labels: correctness
>
> Try the following in SQL shell:
> {code}
> select '\\\\' like '%\\%';
> {code}
> It returned false, which is wrong.
> cc: [~yhuai] [~joshrosen]
> A false-negative considered previously:
> {code}
> select '\\\\' rlike '.*\\\\\\\\.*';
> {code}
> It returned true, which is correct if we assume that the pattern is treated
> as a Java string but not raw string.
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