SQL入门之集合操作

<span style="color: #0000ff">select</span> <span style="color: #ff0000">‘</span><span style="color: #ff0000">IND</span><span style="color: #ff0000">‘</span><span style="color: #000000"> type_cd, cust_id, lname name
</span><span style="color: #0000ff">from</span><span style="color: #000000"> individual
</span><span style="color: #0000ff">union</span> <span style="color: #808080">all</span>
<span style="color: #0000ff">select</span> <span style="color: #ff0000">‘</span><span style="color: #ff0000">BUS</span><span style="color: #ff0000">‘</span><span style="color: #000000"> type_cd, cust_id, name
</span><span style="color: #0000ff">from</span> business;

执行操作后的结果为：

其中，18个数据来自与individual表，8个来自于business。为了更清楚的看到区别，看下面两个实例：

<span style="color: #0000ff">select</span><span style="color: #000000"> a.cust_id, a.name
</span><span style="color: #0000ff">from</span><span style="color: #000000"> business a
uinon </span><span style="color: #808080">all</span>
<span style="color: #0000ff">select</span><span style="color: #000000"> b.cust_id, b.name
</span><span style="color: #0000ff">from</span> business b;

结果为

而

<span style="color: #0000ff">select</span><span style="color: #000000"> a.cust_id, a.name
</span><span style="color: #0000ff">from</span><span style="color: #000000"> business a
</span><span style="color: #0000ff">union</span>
<span style="color: #0000ff">select</span><span style="color: #000000"> b.cust_id, b.name
</span><span style="color: #0000ff">from</span> business b;

结果为

可以很明显看出区别。

1.intersect和except操作符

我用的MySQL版本似乎没有实现这两个功能。：（

SQL入门之集合操作

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