迭代式mysql查询速度变慢

Question

I did a quick set of queries to break this: 27JAN2013 into 2013-01-27 in another field. It was easier just to do 12 in a row changing the month to be written for each. What I noticed is each subsequent query took a little bit longer.

The first:

update 
   hondaacura 
set transdate1 = concat_ws('-',substr(trxdate,6,4),'01', left(trxdate,2)) 
where substr(trxdate,3,3) = 'JAN';  

It took 6.27 to update on a total table size of 3.5 million records.

The February statement running next took 6.9, and so on, until December which took 12.3.

Why would it slow down with each subsequent query?

Answer 1

I think you can solve this with this update statement. Then you don't need to write 12 statements and execute them in a row.

update 
   hondaacura 
set transdate1 = STR_TO_DATE(trxdate, '%d%b%Y');

For more info see here .