diff --git a/src/datatypes/src/json/value.rs b/src/datatypes/src/json/value.rs
index 575271ae7e..e2422ca78d 100644
--- a/src/datatypes/src/json/value.rs
+++ b/src/datatypes/src/json/value.rs
@@ -419,6 +419,19 @@ impl JsonValue {
         helper(self.json_variant)
     }
 
+    /// Recursively aligns this JSON value to `expected` in place. This is to make JSON values fill
+    /// into a [StructArray], which requires a unified static datatype.
+    ///
+    /// Alignment follows these rules:
+    /// - `Null` aligns to any type, and any value aligns to `Null` as `Null`.
+    /// - Numbers are converted only within compatible number categories.
+    /// - Arrays align each element recursively to the expected item type.
+    /// - Objects require `expected` to contain all fields from the current value. Missing expected
+    ///   fields are filled with `Null`.
+    /// - `Variant` preserves the original JSON payload as serialized bytes.
+    ///
+    /// Returns an error if the value cannot be aligned without losing existing object fields or
+    /// when a scalar type conversion is incompatible.
     pub(crate) fn try_align(&mut self, expected: &JsonType) -> Result<()> {
         if self.json_type() == expected {
             return Ok(());
diff --git a/src/datatypes/src/types/json_type.rs b/src/datatypes/src/types/json_type.rs
index f8629b7f17..d296dc4fcb 100644
--- a/src/datatypes/src/types/json_type.rs
+++ b/src/datatypes/src/types/json_type.rs
@@ -225,6 +225,10 @@ impl JsonType {
 
     /// Try to merge this json type with others, error on datatype conflict.
     pub fn merge(&mut self, other: &JsonType) -> Result<()> {
+        if self == other {
+            return Ok(());
+        }
+
         match (&self.format, &other.format) {
             (JsonFormat::Jsonb, JsonFormat::Jsonb) => Ok(()),
             (JsonFormat::Json2(this), JsonFormat::Json2(that)) => {