diff --git a/notes/pics/next-key-locks.png b/notes/pics/next-key-locks.png
new file mode 100644
index 00000000..94cf0dee
Binary files /dev/null and b/notes/pics/next-key-locks.png differ
diff --git a/notes/数据库系统原理.md b/notes/数据库系统原理.md
index ec7b72c6..59006f30 100644
--- a/notes/数据库系统原理.md
+++ b/notes/数据库系统原理.md
@@ -362,6 +362,8 @@ SELECT c FROM t WHERE c BETWEEN 10 and 20 FOR UPDATE;
 (20, +∞)
 ```
 
+<div align="center"> <img src="pics/next-key-locks.png" width="560px"/> </div><br>
+
 ## 七、关系数据库设计理论
 
 ### 函数依赖
diff --git a/tools/diagram/src/next-key-locks.svg b/tools/diagram/src/next-key-locks.svg
new file mode 100644
index 00000000..857ec22f
--- /dev/null
+++ b/tools/diagram/src/next-key-locks.svg
@@ -0,0 +1,59 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="620" height="230" viewBox="0 0 620 230">
+  <style>
+    text { font-family: "PingFang SC", "Microsoft YaHei", Helvetica, Arial, sans-serif; fill: #666; font-size: 12px; }
+    .title { font-weight: bold; font-size: 15px; fill: #777; text-anchor: middle; }
+    .b { font-weight: bold; }
+    .c { text-anchor: middle; }
+    .e { text-anchor: end; }
+    .note { fill: #C0605A; }
+    .ok { fill: #6A9F68; }
+    .sub { font-size: 11px; fill: #888; }
+    .mono { font-family: Menlo, Consolas, monospace; }
+    .arrow { stroke: #666; stroke-width: 1.3; fill: none; marker-end: url(#a); }
+    .red { stroke: #C0605A; marker-end: url(#r); }
+    .green { stroke: #6A9F68; marker-end: url(#g); }
+    .dash { stroke-dasharray: 5 4; }
+    .line { stroke: #666; stroke-width: 1.3; fill: none; }
+    .frame { fill: none; stroke: #999; stroke-width: 1; stroke-dasharray: 4 3; }
+    .shadow { fill: #C0C0C0; }
+  </style>
+  <defs>
+    <marker id="a" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
+      <path d="M1,1 L9,5 L1,9" fill="none" stroke="#666" stroke-width="1.6"/>
+    </marker>
+    <marker id="r" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
+      <path d="M1,1 L9,5 L1,9" fill="none" stroke="#C0605A" stroke-width="1.6"/>
+    </marker>
+    <marker id="g" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
+      <path d="M1,1 L9,5 L1,9" fill="none" stroke="#6A9F68" stroke-width="1.6"/>
+    </marker>
+  </defs>
+  <rect width="100%" height="100%" fill="#FFFFFF"/>
+
+  <text x="310" y="28" class="title">Next-Key Locks</text>
+  <rect x="40" y="106" width="110" height="28" fill="#D8ECF5"/>
+  <text x="95" y="160" class="c mono">(-∞, 10]</text>
+  <rect x="150" y="106" width="105" height="28" fill="#C9E6EC"/>
+  <text x="202.5" y="160" class="c mono">(10, 11]</text>
+  <rect x="255" y="106" width="105" height="28" fill="#D8ECF5"/>
+  <text x="307.5" y="160" class="c mono">(11, 13]</text>
+  <rect x="360" y="106" width="105" height="28" fill="#C9E6EC"/>
+  <text x="412.5" y="160" class="c mono">(13, 20]</text>
+  <rect x="465" y="106" width="115" height="28" fill="#D8ECF5"/>
+  <text x="522.5" y="160" class="c mono">(20, +∞)</text>
+  <line x1="30" y1="120" x2="590" y2="120" class="line"/>
+  <circle cx="150" cy="120" r="6" fill="#61646B"/>
+  <text x="150" y="98" class="c b">10</text>
+  <circle cx="255" cy="120" r="6" fill="#61646B"/>
+  <text x="255" y="98" class="c b">11</text>
+  <circle cx="360" cy="120" r="6" fill="#61646B"/>
+  <text x="360" y="98" class="c b">13</text>
+  <circle cx="465" cy="120" r="6" fill="#61646B"/>
+  <text x="465" y="98" class="c b">20</text>
+  <text x="40" y="98" class="c sub">-∞</text>
+  <text x="580" y="98" class="c sub">+∞</text>
+  <text x="202" y="196" class="c note">Gap Lock (10, 11)</text>
+  <text x="255" y="214" class="c">+ Record Lock 11 = Next-Key Lock (10, 11]</text>
+  <path d="M202,184 L202,166" class="arrow red"/>
+  <text x="310" y="60" class="c sub">索引值 10、11、13、20，每个区间前开后闭</text>
+</svg>