如何向现有数据库中的特定列添加信息

Question

I have a database named week1 which includes columns: age, address, voternum, voterhistory, status, gender, precinct, county, and zip5 .

The information for all rows excluding voterhistory is already in the table!

I need to import the voterhistory column separately from a text file named vhist into the table where voternum of the week1 table is equal to voternum of the vhist text file.

Multiple lines from the text file can be put into the voterhistory column and should be separated by a comma.

For example:

Within week1 there is a person with voternum = 1234 .
In the vhist text file there are 3 records where voternum = 1234 .

One has a voterhistory = 2011 , one has a voterhistory = 2012 , and one has a voterhistory = 2013 .

This means when importing the vhist text file those 3 records should import into the voterhistory column of the week1 table like so: 2011, 2012, 2013 .

Sorry if this sounds confusing, but it's the only way I know how to explain it. If you need further information please let me know.

Answer 1

In MySQL we have a function called CONCAT_WS() It basically concatenates string values using a specified separator. Take a look at the link.

I would use a temp table to load vhist into memory.Then join table week1 to the temp table vhistory and update week1 based on the key matches. That gets you out of having to implement conditional logic in your SQL join.

In code it will look something like this, you may have to work on this a bit to get it to run:

CREATE TEMPORARY TABLE vhistory  (
     voternum VARCHAR(10) NOT NULL
    , voterhistory VARCHAR(10)
   );

LOAD DATA LOCAL INFILE '/path/vhist.txt' INTO TABLE vhistory;


UPDATE week1 SET voterhistory=SELECT CONCAT_WS(SELECT ',',voterhistory FROM vhistory
WHERE week1-voternum = vhistory-voternum );

I did not run this code as I don't have your data.