# mysql语句部分 # \# MySQL中，not in子查询 ``` <pre class="calibre13">``` select <span class="token5">ID</span> <span class="token2">as</span> id<span class="token1">,</span> <span class="token5">TYPE_CODE</span> <span class="token2">as</span> typeCode <span class="token1">,</span> <span class="token5">TYPE_NAME</span> <span class="token2">as</span> typeName <span class="token1">,</span> <span class="token5">PARENT_ID</span> <span class="token2">as</span> parentsId <span class="token1">,</span> <span class="token5">STYLE</span> <span class="token2">as</span> style <span class="token1">,</span> <span class="token5">LEVELS</span> <span class="token2">as</span> levels <span class="token2">from</span> type_code where <span class="token5">PARENT_ID</span> <span class="token">=</span> <span class="token4">'30119a0e-2f57-473d-9f1d-2843561e9064'</span> and <span class="token5">ID</span> not <span class="token2">in</span> <span class="token1">(</span> select <span class="token5">PARENT_ID</span> <span class="token2">from</span> type_code where <span class="token5">PARENT_ID</span><span class="token1">)</span><span class="token1">;</span> ``` ``` 结果满足查询的条件为空…… 后来发现，子查询中存在字段的某些值为null，所以导致了count=0. 所以，将SQL调整为如下： ``` <pre class="calibre13">``` select <span class="token5">ID</span> <span class="token2">as</span> id<span class="token1">,</span> <span class="token5">TYPE_CODE</span> <span class="token2">as</span> typeCode <span class="token1">,</span> <span class="token5">TYPE_NAME</span> <span class="token2">as</span> typeName <span class="token1">,</span> <span class="token5">PARENT_ID</span> <span class="token2">as</span> parentsId <span class="token1">,</span> <span class="token5">STYLE</span> <span class="token2">as</span> style <span class="token1">,</span> <span class="token5">LEVELS</span> <span class="token2">as</span> levels <span class="token2">from</span> type_code where <span class="token5">PARENT_ID</span> <span class="token">=</span> <span class="token4">'30119a0e-2f57-473d-9f1d-2843561e9064'</span> and <span class="token5">ID</span> not <span class="token2">in</span> <span class="token1">(</span> select <span class="token5">PARENT_ID</span> <span class="token2">from</span> type_code where <span class="token5">PARENT_ID</span> is not <span class="token2">null</span><span class="token1">)</span><span class="token1">;</span> ``` ``` 这样就能正确的查出结果了！ **总结：MySQL中如果要用not in在子查询中限制结果，那必须要将子查询的结果集限制为不含null，不然查询结果count = 0.**