alter table 的功能是修改表格。包括重名命,加減字段,修改字段類型和大小,處理 限制等等。本例子之處理表名和字段,代碼如下:
![](https://img.laitimes.com/img/_0nNw4CM6IyYiwiM6ICdiwiIml2ZuUmbv50LcNncvRXYjlGZul0ZulmbpxGd190LcdmbpRHanlGbodWaohXY05Wez9CX0Vmbu4GZzNmLzV2Zh1Wavw1LcpDc0RHaiojIsJye.gif)
create table liu(a varchar2 ( 20 ),b number ( 2 ))
![](https://img.laitimes.com/img/_0nNw4CM6IyYiwiM6ICdiwiIml2ZuUmbv50LcNncvRXYjlGZul0ZulmbpxGd190LcdmbpRHanlGbodWaohXY05Wez9CX0Vmbu4GZzNmLzV2Zh1Wavw1LcpDc0RHaiojIsJye.gif)
![](https://img.laitimes.com/img/_0nNw4CM6IyYiwiM6ICdiwiIml2ZuUmbv50LcNncvRXYjlGZul0ZulmbpxGd190LcdmbpRHanlGbodWaohXY05Wez9CX0Vmbu4GZzNmLzV2Zh1Wavw1LcpDc0RHaiojIsJye.gif)
alter table liu rename to jin
![](https://img.laitimes.com/img/_0nNw4CM6IyYiwiM6ICdiwiIml2ZuUmbv50LcNncvRXYjlGZul0ZulmbpxGd190LcdmbpRHanlGbodWaohXY05Wez9CX0Vmbu4GZzNmLzV2Zh1Wavw1LcpDc0RHaiojIsJye.gif)
rename jin to cai
![](https://img.laitimes.com/img/_0nNw4CM6IyYiwiM6ICdiwiIml2ZuUmbv50LcNncvRXYjlGZul0ZulmbpxGd190LcdmbpRHanlGbodWaohXY05Wez9CX0Vmbu4GZzNmLzV2Zh1Wavw1LcpDc0RHaiojIsJye.gif)
![](https://img.laitimes.com/img/_0nNw4CM6IyYiwiM6ICdiwiIml2ZuUmbv50LcNncvRXYjlGZul0ZulmbpxGd190LcdmbpRHanlGbodWaohXY05Wez9CX0Vmbu4GZzNmLzV2Zh1Wavw1LcpDc0RHaiojIsJye.gif)
alter table cai add c varchar2 ( 30 )
![](https://img.laitimes.com/img/_0nNw4CM6IyYiwiM6ICdiwiIml2ZuUmbv50LcNncvRXYjlGZul0ZulmbpxGd190LcdmbpRHanlGbodWaohXY05Wez9CX0Vmbu4GZzNmLzV2Zh1Wavw1LcpDc0RHaiojIsJye.gif)
alter table cai add (d varchar2 ( 30 ),e number ( 4 ))
![](https://img.laitimes.com/img/_0nNw4CM6IyYiwiM6ICdiwiIml2ZuUmbv50LcNncvRXYjlGZul0ZulmbpxGd190LcdmbpRHanlGbodWaohXY05Wez9CX0Vmbu4GZzNmLzV2Zh1Wavw1LcpDc0RHaiojIsJye.gif)
![](https://img.laitimes.com/img/_0nNw4CM6IyYiwiM6ICdiwiIml2ZuUmbv50LcNncvRXYjlGZul0ZulmbpxGd190LcdmbpRHanlGbodWaohXY05Wez9CX0Vmbu4GZzNmLzV2Zh1Wavw1LcpDc0RHaiojIsJye.gif)
alter table cai rename column e to f
![](https://img.laitimes.com/img/_0nNw4CM6IyYiwiM6ICdiwiIml2ZuUmbv50LcNncvRXYjlGZul0ZulmbpxGd190LcdmbpRHanlGbodWaohXY05Wez9CX0Vmbu4GZzNmLzV2Zh1Wavw1LcpDc0RHaiojIsJye.gif)
![](https://img.laitimes.com/img/_0nNw4CM6IyYiwiM6ICdiwiIml2ZuUmbv50LcNncvRXYjlGZul0ZulmbpxGd190LcdmbpRHanlGbodWaohXY05Wez9CX0Vmbu4GZzNmLzV2Zh1Wavw1LcpDc0RHaiojIsJye.gif)
alter table cai modify d varchar ( 40 )
![](https://img.laitimes.com/img/_0nNw4CM6IyYiwiM6ICdiwiIml2ZuUmbv50LcNncvRXYjlGZul0ZulmbpxGd190LcdmbpRHanlGbodWaohXY05Wez9CX0Vmbu4GZzNmLzV2Zh1Wavw1LcpDc0RHaiojIsJye.gif)
alter table cai modify f varchar ( 40 )
![](https://img.laitimes.com/img/_0nNw4CM6IyYiwiM6ICdiwiIml2ZuUmbv50LcNncvRXYjlGZul0ZulmbpxGd190LcdmbpRHanlGbodWaohXY05Wez9CX0Vmbu4GZzNmLzV2Zh1Wavw1LcpDc0RHaiojIsJye.gif)
![](https://img.laitimes.com/img/_0nNw4CM6IyYiwiM6ICdiwiIml2ZuUmbv50LcNncvRXYjlGZul0ZulmbpxGd190LcdmbpRHanlGbodWaohXY05Wez9CX0Vmbu4GZzNmLzV2Zh1Wavw1LcpDc0RHaiojIsJye.gif)
alter table cai drop column f