sqlite并不支持建表后修改主键，或删除列，如果要修改，请参考如下做法：

(11) How do I add or delete columns from an existing table in sqlite.

sqlite has limitedALTER TABLEsupport that you can use to add a column to the end of a table or to change the name of a table. If you want to make more complex changes in the structure of a table,you will have to recreate the table. You can save existing data to a temporary table,drop the old table,create the new table,then copy the data back in from the temporary table.

For example,suppose you have a table named "t1" with columns names "a","b",and "c" and that you want to delete column "c" from this table. The following steps illustrate how this could be done:

BEGIN TRANSACTION;
CREATE TEMPORARY TABLE t1_backup(a,b);
INSERT INTO t1_backup SELECT a,b FROM t1;
DROP TABLE t1;
CREATE TABLE t1(a,b);
INSERT INTO t1 SELECT a,b FROM t1_backup;
DROP TABLE t1_backup;
COMMIT;

http://sqlite.org/faq.html#q11

http://stackoverflow.com/questions/946011/sqlite-add-primary-key