MySQL将错误的数据类型导入VARCHAR列

Question

Today I did something stupid: I had a list of card numbers in an excel file that I had to import to a DB table somehow. So i exported the numbers to CSV file, but without any quotes (don't ask me why). The file looked like:

123456
234567
345678
...

Then I created a table with a single VARCHAR(22) column and did a

LOAD DATA LOCAL INFILE 'numbers.csv' INTO TABLE cards

This worked fine, apart from many warnings, which I ignored (the other stupid thing I did). After that I tried to query with this SQL:

SELECT * FROM cards WHERE number='123456'

which gave me an empty result. Whereas this works:

SELECT * FROM cards WHERE number=123456

Notice the missing quotes! So it seems, that I managed to populate my VARCHAR table with INTEGER data. I have no idea how that is possible at all.

I already tried to fix this with an UPDATE like this

UPDATE cards SET number = CAST(number AS CHAR(22))

But that didn't work.

So is there a way to fix this and how could this even happen?

Answer 1

This is the result of some implicit conversion in order to do a numerical comparison:

SELECT * FROM cards WHERE number='123'

This will only match against text fields that are literally "123" and will miss on " 123" and "123\\r" if you have those. For some reason, "123 " and "123" are considered "equivalent" presumably do to trailing space removal on both sides.

When doing your import, don't forget LINES TERMINATED BY '\\r\\n' . If you're ever confused about what's in a field, including hidden characters, try:

SELECT HEX(number) FROM cards

This will show the hex-dumped output of each string. Things like 20 indicate space, just as %20 in a URL is a space.

You can also fix this by:

UPDATE cards SET number=REPLACE(number, '\r', '')