sqlite应用之路---删除列
1.思路
（1）我们通过临时表来实现，首先我们创建和目标表结构的临时表（除去要删除的字段）；
（2）把目标表中的数据放入临时表；
（3）然后我们将目标表删除（drop），并重新创建（除去要删除的字段，和原来的目标表结构一样）；
（4）我们把临时表中的数据放回目标表，并删除临时表。
2.例子
目标表target_table(id int primary key,nametext,sex text,age int);
//其中sex字段是要被删除的字段
步骤（1）：创建临时表
create temp table temp_target_table(id int primary key,name text,age int);
步骤（2）：保存数据
insert into temp_target_table(id,name,age)select id,age from target_table
步骤（3）删除目标表，并重创建
drop table target_table;
create table target_table(id int primarykey,age int);
步骤（4）将数据放回目标表，并删除临时表
insert into target_table(id,age from temp_target_table;
drop table temp_target_table;
3.来自官网
sqlite，关于删除字段这一点，这里我放上sqlite官网上的解释：
（我是一个链接）
sqlite has limitedALTERTABLEsupport that you can use to add a column to the end of atable or to change the name of a table. If you want to make more complexchanges in the structure of a table,you will have to recreate the table. Youcan save existing data to a temporary table,drop the old table,create the newtable,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 bedone:
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;
