# mysql語句部分 # \# MySQL中，not in子查詢 ``` <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> ``` ``` 結果滿足查詢的條件為空…… 后來發現，子查詢中存在字段的某些值為null，所以導致了count=0. 所以，將SQL調整為如下： ``` <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> ``` ``` 這樣就能正確的查出結果了！ **總結：MySQL中如果要用not in在子查詢中限制結果，那必須要將子查詢的結果集限制為不含null，不然查詢結果count = 0.**