SQLite date split - sqlite

Question

In SQLite, I have a 'date' field that's varchar(20), as an example dates currently read '12-AUG-15'. I need to split the date field into 4 separate fields: 'day', 'month', 'year', and 'month_num'. Problem is I don't know how to convert month names into numbers as well as the year into a 4 digit year. I'm thinking of using case and string concatenation functions? Any advice how to start it is well appreciated.

Answer 1

SQLite has very limited date and string functions. The date functions understand ISO 8601. You're better off in the long run converting to ISO 8601 and then using the date functions. It will sort better, and most everything understands ISO 8601 format.
SQLite doesn't have an easy way to do this, but you can write a user defined function to do the conversion. Most SQLite drivers allow you to write it in whatever language you're using. Here's an example in Ruby.
require "sqlite3"
require "date"
# Open a database
db = SQLite3::Database.new "test.db"
# Create a SQLite function date_to_iso()
db.create_function( "date_to_iso", 1 ) do |proxy, date|
# Convert 12-AUG-15 to 2015-08-12 (ISO 8601 format)
iso = Date.strptime(date, "%d-%b-%y");
# This is how you return the result via a FunctionProxy
proxy.result = iso.to_s
end
# Now you can use date_iso_iso() in SQLite queries in this process.
db.execute("UPDATE stuff SET date = date_to_iso(date)")
Then you can use strftime to query the individual date parts.
select
strftime("%d", date) as day,
strftime("%m", month) as month,
strftime("%Y", year) as year
from whatever;
Unfortunately, SQLite doesn't have a way to convert to the month name. You could write a big CASE statement.
select case strftime("%m", month)
when 1 then 'JAN'
when 2 then 'FEB'
...
end
from whatever;
Or you could add another user defined function to do the conversion.
But since you now have a standard date format, it's probably better to just return the whole ISO 8601 date and let the application do what it wants with it.