Question

In SQLite 3

If I update a field that has a full-text index, will the full text index get updated, or do I need to get it to update manually?

Answer 1

It depends, for exmaple.
It won’t update automatically if you are using “External Content FTS4 Tables”.

from http://www.sqlite.org/fts3.html#section_6_2_2

CREATE TABLE t2(id INTEGER PRIMARY KEY, a, b, c, d);
CREATE VIRTUAL TABLE t3 USING fts4(content="t2", b, c);

INSERT INTO t2 VALUES(2, 'a b', 'c d', 'e f');
INSERT INTO t2 VALUES(3, 'g h', 'i j', 'k l');
INSERT INTO t3(docid, b, c) SELECT id, b, c FROM t2;
-- The following query returns a single row with two columns containing
-- the text values "i j" and "k l".
--
-- The query uses the full-text index to discover that the MATCH 
-- term matches the row with docid=3. It then retrieves the values
-- of columns b and c from the row with rowid=3 in the content table
-- to return.
--
SELECT * FROM t3 WHERE t3 MATCH 'k';

-- Following the UPDATE, the query still returns a single row, this
-- time containing the text values "xxx" and "yyy". This is because the
-- full-text index still indicates that the row with docid=3 matches
-- the FTS4 query 'k', even though the documents stored in the content
-- table have been modified.
--
UPDATE t2 SET b = 'xxx', c = 'yyy' WHERE rowid = 3;
SELECT * FROM t3 WHERE t3 MATCH 'k';

but it can be solve via trigger too.

Instead of writing separately to the full-text index and the content
table, some users may wish to use database triggers to keep the
full-text index up to date with respect to the set of documents stored
in the content table. For example, using the tables from earlier
examples: