mysql将表a中查询的数据插入到表b中

如果表b存在

1

<code class=sql><code class=sql><code class=sql>insert into b select * from a;</code></code></code>

如果表b不存在

1

<code class=sql><code class=sql><code class=sql><code class=sql><code class=sql><code class=sql>create table b as select * from a;</code></code></code></code></code></code>

扩展：

将b表中的某写字段值插入到a表中

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<code class=sql><code class=sql><code class=sql><code class=sql><code class=sql><code class=sql><code class=sql><code class=sql><code class=sql><code class=sql><code class=sql>insert into a (userid,username) select b.userid,b.username from tr_ajax_chat_messages;</code></code></code></code></code></code></code></code></code></code></code>

将a表和b表userid相等的值保存到a表

1<code class=sql><code class=sql><code class=sql><code class=sql><code class=sql><code class=sql><code class=sql><code class=sql><code class=sql><code class=sql><code class=sql><code class=sql><code class=sql><code class=sql><code class=sql><code class=sql><code class=sql><code class=sql>update a set a.username=(select b.username from b where a.userid = b.userid);</code></code></code></code></code></code></code></code></code></code></code></code></code></code></code></code></code></code>，

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