sql null

haunt98 · Jan 11, 2025 · 0c7cefa · 0c7cefa
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diff --git a/docs/2022-07-31-sql.html b/docs/2022-07-31-sql.html
@@ -283,7 +283,11 @@ <h2 class="heading-element">Be careful with NULL</h2>
 <span class="pl-k">FROM</span> table
 <span class="pl-k">WHERE</span> (field_something IS <span class="pl-k">NULL</span> <span class="pl-k">OR</span> field_something <span class="pl-k">!=</span> <span class="pl-c1">1</span>)</pre>
     </div>
-    <p>Need clarify why this happen? Idk :(</p>
+    <p>
+      Because <code>NULL</code> is not equal to anything, even
+      <code>NULL != NULL</code>, we only can check with <code>IS NULL</code> or
+      <code>IS NOT NULL</code>.
+    </p>
     <div class="markdown-heading">
       <h2 class="heading-element"><code>VARCHAR</code> or <code>TEXT</code></h2>
       <a
@@ -516,9 +520,25 @@ <h2 class="heading-element">Thanks</h2>
           <a
             href="https://www.depesz.com/2024/12/01/sql-best-practices-dont-compare-count-with-0/"
             rel="nofollow"
-            >SQL best practices – don’t compare count(*) with 0</a
+            >SQL best practices – don’t compare count with 0</a
+          >
+        </p>
+      </li>
+      <li>
+        <p>
+          <a
+            href="https://jirevwe.github.io/sql-nulls-are-weird.html"
+            rel="nofollow"
+            >SQL NULLs are Weird!</a
           >
         </p>
+        <ul>
+          <li>
+            <a href="https://www.sqlite.org/nulls.html" rel="nofollow"
+              >NULL Handling in SQLite Versus Other Database Engines</a
+            >
+          </li>
+        </ul>
       </li>
     </ul>
 

diff --git a/posts/2022-07-31-sql.md b/posts/2022-07-31-sql.md
@@ -131,7 +131,8 @@ FROM table
 WHERE (field_something IS NULL OR field_something != 1)
 ```
 
-Need clarify why this happen? Idk :(
+Because `NULL` is not equal to anything, even `NULL != NULL`, we only can check
+with `IS NULL` or `IS NOT NULL`.
 
 ## `VARCHAR` or `TEXT`
 
@@ -192,4 +193,6 @@ FROM information_schema.statistics;
 - [Difference between text and varchar (character varying)](https://stackoverflow.com/a/4849030)
 - [How to get the number of total results when there is LIMIT in query?](https://stackoverflow.com/q/33889922)
 - [Run a query with a LIMIT/OFFSET and also get the total number of rows](https://stackoverflow.com/q/28888375)
-- [SQL best practices – don’t compare count(*) with 0](https://www.depesz.com/2024/12/01/sql-best-practices-dont-compare-count-with-0/)
+- [SQL best practices – don’t compare count with 0](https://www.depesz.com/2024/12/01/sql-best-practices-dont-compare-count-with-0/)
+- [SQL NULLs are Weird!](https://jirevwe.github.io/sql-nulls-are-weird.html)
+  - [NULL Handling in SQLite Versus Other Database Engines](https://www.sqlite.org/nulls.html)