title: Populate a SQL table column based on other values in table
body: <p>I have table that is already populated with the tweets. I am reading some dictionaries from the tweet using json. I am using SQLite3 in Python. </p>
  
  <pre><code>TwTbl = """Create table TwTbl
  (created_at text, id text, geo_count integer, user_id integer, text text, geo_id integer, source text,in_reply_to_user_id integer, retweet_count integer,
  constraint fk_UserEntry
  foreign key (user_id) references UserEntry(id)
  constraint fk_Geo
  foreign key (geo_count) references Geo(Id)
  );"""   
  c.execute(TwTbl) 
  </code></pre>
  
  <p>Now I have to add a column to this table "LenTweet" which is supposed to contain the length of coloumn "Text". I can add the coloumn using </p>
  
  <pre><code>c.execute("ALTER TABLE TwTbl ADD LenTweet text").fetchall()
  </code></pre>
  
  <p>But, I do not know how to populate this newly created coloumn with the length of "Text" column. All I can think of is to recreate the table and insert the length right there, while reading the tweets. The coloumn has to be populated based on the values that are in the table currently. This does not get triggered with any inserts. Can someone please tell me a way, so I can populate the table with the data that I have already in it?
  Thanks in advance.</p>