在sqlite中alter table 是无法实现对字段的添加或修改的

如：ALTER TABLE table_name ADD column_name datatype 这个语句在sqlite中无效

对于这问题，sqlite官方给出这样的解答，基本就是只能通过创建一张临时表，来修改字段

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

sqlite has limited ALTER TABLE support 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;