The mysqldump plus w parameter is something to look out for when backing up data

When we use mysqldump to back up data, we have the option "where / -w". We can specify the backup conditions.

-w, --where=name Dump only selected records. Quotes are mandatory

We can do a test like this:

mysqldump --single-transaction -w ' id < 10000 ' mydb mytable > mydump.sql

At this point, you can back up id in the mytable table < All records of 10000. Suppose we want to add another time range condition, for example:

mysqldump --single-transaction -w " id < 10000 and logintime < unix_timestamp('2014-06-01')" mydb mytable > mydump.sql

Here, 1 pay attention to single and double quotation marks to avoid this situation:

mysqldump --single-transaction -w ' id < 10000 and logintime < unix_timestamp('2014-06-01') ' mydb mytable > mydump.sql

In this case, the resulting condition is resolved to:

WHERE id < 10000 and logintime < unix_timestamp(2014-06-01)

Eagle-eyed students will find that the time conditions become:

WHERE id < 10000 and logintime < unix_timestamp(2014-06-01)

So it becomes:

unix_timestamp(2007)

This is quite different from what we thought, so be careful