fix cosine_distance docs (oceanbase#464)

docs/docs/game/miniob-vectordb.md

@@ -54,7 +54,7 @@ select embedding + '[1.5,2.3,3.3]', embedding - '[1,2,3]', '[1,2,3]' - embedding
 
   * cosine_distance：
     * 语法：cosine_distance(vector A, vector B)
-    * 计算公式：$[ D = \frac{\mathbf{A} \cdot \mathbf{B}}{|\mathbf{A}| |\mathbf{B}|} = \frac{\sum_{i=1}^{n} A_i B_i}{\sqrt{\sum_{i=1}^{n} A_i^2} \sqrt{\sum_{i=1}^{n} B_i^2}} ]$
+    * 计算公式：$[ D = 1 - \frac{\mathbf{A} \cdot \mathbf{B}}{|\mathbf{A}| |\mathbf{B}|} = 1 - \frac{\sum_{i=1}^{n} A_i B_i}{\sqrt{\sum_{i=1}^{n} A_i^2} \sqrt{\sum_{i=1}^{n} B_i^2}} ]$
 
   * inner_product：
     * 语法：inner_product(vector A, vector B)