SQLite学习——ALTER TABLE操作限制

1. SQLite不支持对列的改名和修改类型等操作，想要操作官方给出的方法是先备份原表数据到临时表，然后删除原表，再创建新的表结构，然后导入临时表的数据，官方解释如下：(11) How do I add or delete columns from an existing table inSQLite.
   

   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;

2. 推荐几个学习SQLite有用的官方链接：

   http://www.sqlite.org/syntaxdiagrams.html#column-def

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

（编辑：李大同）

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