创建、删除和修改表的DDL语句

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<h2><a name="t0"></a>一、新建表</h2>
<h3><a name="t1"></a>1.1 新建表增加列级主键约束</h3>
<div><pre onclick="hljs.copyCode(event)"><code class="language-sql hljs"><span class="hljs-keyword">create</span> <span class="hljs-keyword">table</span> mydept(dept_id <span class="hljs-built_in">number</span> <span class="hljs-keyword">constraint</span> pk_dept_id primary <span class="hljs-keyword">key</span>,dept_name varchar2(<span class="hljs-number">20</span>));</code><div class="hljs-button" data-title="复制"></div></pre>
<h3><a name="t2"></a>1.2 新建表增加表级主键约束</h3>
<div><pre onclick="hljs.copyCode(event)"><code class="language-sql hljs"><span class="hljs-keyword">create</span> <span class="hljs-keyword">table</span> mydept(dept_id <span class="hljs-built_in">number</span>,dept_name varchar2(<span class="hljs-number">20</span>),<span class="hljs-keyword">constraint</span> pk_dept_id primary <span class="hljs-keyword">key</span>(dept_id));</code><div class="hljs-button" data-title="复制"></div></pre>
<h2><a name="t3"></a>二、删除表</h2>
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<div><pre onclick="hljs.copyCode(event)"><code class="language-sql hljs"><span class="hljs-keyword">drop</span> <span class="hljs-keyword">table</span> mydept;</code><div class="hljs-button" data-title="复制"></div></pre>
<h2><a name="t4"></a>三、修改表</h2>
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<h3><a name="t5"></a>3.1 增加一个字段loc</h3>
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<div><pre onclick="hljs.copyCode(event)"><code class="language-sql hljs"><span class="hljs-keyword">alter</span> <span class="hljs-keyword">table</span> mydept <span class="hljs-keyword">add</span> loc varchar2(<span class="hljs-number">30</span>);</code><div class="hljs-button" data-title="复制"></div></pre>
<h3><a name="t6"></a>3.2 重命名字段loc为location</h3>
<pre onclick="hljs.copyCode(event)"><code class="language-sql hljs"><span class="hljs-keyword">alter</span> <span class="hljs-keyword">table</span> mydept <span class="hljs-keyword">rename</span> <span class="hljs-keyword">column</span> loc <span class="hljs-keyword">to</span> location;</code><div class="hljs-button" data-title="复制"></div></pre>
<h3><a name="t7"></a>3.3 修改字段location数据类型</h3>
<pre onclick="hljs.copyCode(event)"><code class="language-sql hljs"><span class="hljs-keyword">alter</span> <span class="hljs-keyword">table</span> mydept <span class="hljs-keyword">modify</span> location varchar2(<span class="hljs-number">10</span>);</code><div class="hljs-button" data-title="复制"></div></pre>
<h3><a name="t8"></a>3.4 删除字段</h3>
<pre onclick="hljs.copyCode(event)"><code class="language-sql hljs"><span class="hljs-keyword">alter</span> <span class="hljs-keyword">table</span> mydept <span class="hljs-keyword">drop</span> <span class="hljs-keyword">column</span> location;</code><div class="hljs-button" data-title="复制"></div></pre>
<h3><a name="t9"></a>3.5 增加主键约束</h3>
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<div><pre onclick="hljs.copyCode(event)"><code class="language-sql hljs"><span class="hljs-keyword">alter</span> <span class="hljs-keyword">table</span> mydept <span class="hljs-keyword">add</span> <span class="hljs-keyword">constraint</span> pk_dept_id primary <span class="hljs-keyword">key</span>(dept_id);</code><div class="hljs-button" data-title="复制"></div></pre>
<h3><a name="t10"></a>3.6 删除主键约束</h3>
<pre onclick="hljs.copyCode(event)"><code class="language-sql hljs"><span class="hljs-keyword">alter</span> <span class="hljs-keyword">table</span> mydept <span class="hljs-keyword">drop</span> <span class="hljs-keyword">constraint</span> pk_dept_id;</code><div class="hljs-button" data-title="复制"></div></pre>
<h3><a name="t11"></a>3.7 增加外键约束</h3>
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<div><pre onclick="hljs.copyCode(event)"><code class="language-delphi hljs">alter table mydept add constraint fk_dept_id foreign key(dept_id) references dept(deptno);</code><div class="hljs-button" data-title="复制"></div></pre><br><br></div>
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