Fix ALTER deparser dispatch for inactive column metadata

src/main/java/net/sf/jsqlparser/statement/alter/AlterConstraintAttributes.java

@@ -38,6 +38,16 @@ public List<ColumnIdentityAction> getColumnIdentityActions() {
         return Collections.emptyList();
     }
 
+    @Override
+    protected boolean usesColumnActionBody() {
+        return false;
+    }
+
+    @Override
+    public boolean hasActiveColumnDefinitions() {
+        return false;
+    }
+
     @Override
     public boolean hasActiveTableDefinition() {
         return false;

src/main/java/net/sf/jsqlparser/statement/alter/AlterExpression.java

@@ -482,8 +482,7 @@ public List<ColumnSetDefault> getColumnSetDefaultList() {
      * existing action-specific API to add or remove entries.
      */
     public List<ColumnDefaultAction> getColumnDefaults() {
-        if (operation != AlterOperation.ALTER || columnSetDefaultList == null
-                || constraintType != null && constraintSymbol != null
+        if (!usesColumnActionBody() || columnSetDefaultList == null
                 || columnDropDefaultList != null && !columnDropDefaultList.isEmpty()) {
             return Collections.emptyList();
         }
@@ -1077,7 +1076,7 @@ protected void appendBody(StringBuilder b) {
             b.append(optionalSpecifier);
         } else if (hasExplicitConstraintHeader()) {
             toStringConstraintAlter(b);
-        } else if (hasAlterColumnValueActions()) {
+        } else if (usesColumnActionBody()) {
             toStringAlterColumn(b);
         } else if (isSimpleKeywordOperation()) {
             toStringSimpleKeyword(b);
@@ -1101,6 +1100,32 @@ private boolean hasAlterColumnValueActions() {
                         || columnSetVisibilityList != null && !columnSetVisibilityList.isEmpty());
     }
 
+    /**
+     * Whether the selected body renders ALTER COLUMN default or visibility actions. Subclasses
+     * overriding {@link #appendBody(StringBuilder)} must reflect their dispatch here as well.
+     */
+    protected boolean usesColumnActionBody() {
+        return hasAlterColumnValueActions() && !hasExplicitConstraintHeader();
+    }
+
+    /**
+     * Whether this action currently renders its column definitions through the general body.
+     * Inactive column metadata is retained in the AST but must not select a different body when
+     * deparsing. Subclasses with their own body dispatch override this method accordingly.
+     */
+    public boolean hasActiveColumnDefinitions() {
+        return hasColumnDefinitionPayload() && operation != AlterOperation.UNSPECIFIC
+                && !hasExplicitConstraintHeader() && !usesColumnActionBody()
+                && !isSimpleKeywordOperation() && !isRenameOperation() && !isDropSpecialOperation()
+                && operation != AlterOperation.CONVERT && operation != AlterOperation.COLLATE
+                && !isPartitionOperation();
+    }
+
+    /** Whether column definitions take precedence within the general body. */
+    protected boolean hasColumnDefinitionPayload() {
+        return commentText == null && columnName == null && colDataTypeList != null;
+    }
+
     /**
      * Appends the common tail (parameters, index comment) shared by all ALTER expressions.
      */

src/main/java/net/sf/jsqlparser/statement/alter/AlterExpressionCharset.java

@@ -25,6 +25,16 @@ public List<ColumnIdentityAction> getColumnIdentityActions() {
         return Collections.emptyList();
     }
 
+    @Override
+    protected boolean usesColumnActionBody() {
+        return false;
+    }
+
+    @Override
+    public boolean hasActiveColumnDefinitions() {
+        return false;
+    }
+
     @Override
     public boolean hasActiveTableDefinition() {
         return false;

src/main/java/net/sf/jsqlparser/statement/alter/AlterExpressionDrop.java

@@ -24,6 +24,17 @@ public List<ColumnIdentityAction> getColumnIdentityActions() {
         return getColumnIdentityActionsFromDefinitions();
     }
 
+    @Override
+    protected boolean usesColumnActionBody() {
+        return false;
+    }
+
+    @Override
+    public boolean hasActiveColumnDefinitions() {
+        return hasColumnDefinitionPayload() && !isDropSpecialOperation()
+                && getOperation() != AlterOperation.DROP_PARTITION;
+    }
+
     @Override
     public boolean hasActiveTableDefinition() {
         return false;

src/main/java/net/sf/jsqlparser/statement/alter/AlterExpressionOrderBy.java

@@ -35,6 +35,16 @@ public List<ColumnIdentityAction> getColumnIdentityActions() {
         return Collections.emptyList();
     }
 
+    @Override
+    protected boolean usesColumnActionBody() {
+        return false;
+    }
+
+    @Override
+    public boolean hasActiveColumnDefinitions() {
+        return false;
+    }
+
     @Override
     public boolean hasActiveTableDefinition() {
         return false;

src/main/java/net/sf/jsqlparser/statement/alter/AlterExpressionPartition.java

@@ -270,6 +270,16 @@ public List<ColumnIdentityAction> getColumnIdentityActions() {
         return Collections.emptyList();
     }
 
+    @Override
+    protected boolean usesColumnActionBody() {
+        return false;
+    }
+
+    @Override
+    public boolean hasActiveColumnDefinitions() {
+        return false;
+    }
+
     @Override
     public boolean hasActiveTableDefinition() {
         return false;

src/main/java/net/sf/jsqlparser/statement/alter/AlterExpressionPrimaryKey.java

@@ -39,6 +39,16 @@ public List<ColumnIdentityAction> getColumnIdentityActions() {
         return Collections.emptyList();
     }
 
+    @Override
+    protected boolean usesColumnActionBody() {
+        return false;
+    }
+
+    @Override
+    public boolean hasActiveColumnDefinitions() {
+        return false;
+    }
+
     @Override
     public boolean hasActiveTableDefinition() {
         return false;

src/main/java/net/sf/jsqlparser/statement/alter/AlterExpressionRename.java

@@ -50,6 +50,16 @@ public List<ColumnIdentityAction> getColumnIdentityActions() {
         return Collections.emptyList();
     }
 
+    @Override
+    protected boolean usesColumnActionBody() {
+        return false;
+    }
+
+    @Override
+    public boolean hasActiveColumnDefinitions() {
+        return getOperation() == AlterOperation.RENAME && hasColumnDefinitionPayload();
+    }
+
     @Override
     public boolean hasActiveTableDefinition() {
         return false;

src/main/java/net/sf/jsqlparser/statement/alter/AlterExpressionTableOption.java

@@ -41,6 +41,16 @@ public List<ColumnIdentityAction> getColumnIdentityActions() {
         return Collections.emptyList();
     }
 
+    @Override
+    protected boolean usesColumnActionBody() {
+        return false;
+    }
+
+    @Override
+    public boolean hasActiveColumnDefinitions() {
+        return false;
+    }
+
     @Override
     public boolean hasActiveTableDefinition() {
         return false;

src/main/java/net/sf/jsqlparser/statement/alter/AlterForeignDataOptions.java

@@ -47,6 +47,16 @@ public List<ColumnIdentityAction> getColumnIdentityActions() {
         return Collections.emptyList();
     }
 
+    @Override
+    protected boolean usesColumnActionBody() {
+        return false;
+    }
+
+    @Override
+    public boolean hasActiveColumnDefinitions() {
+        return false;
+    }
+
     @Override
     public boolean hasActiveTableDefinition() {
         return false;

src/main/java/net/sf/jsqlparser/statement/alter/RelationAlterAction.java

@@ -246,6 +246,16 @@ public List<ColumnIdentityAction> getColumnIdentityActions() {
         return Collections.emptyList();
     }
 
+    @Override
+    protected boolean usesColumnActionBody() {
+        return false;
+    }
+
+    @Override
+    public boolean hasActiveColumnDefinitions() {
+        return false;
+    }
+
     @Override
     public boolean hasActiveTableDefinition() {
         return false;

src/main/java/net/sf/jsqlparser/util/deparser/AlterDeParser.java

@@ -89,7 +89,7 @@ private void deParseAction(AlterExpression action) {
                     expression -> expression.accept(expressionVisitor, null));
             return;
         }
-        if (action.getColDataTypeList() != null) {
+        if (action.hasActiveColumnDefinitions()) {
             action.appendColumnDefinitionsTo(builder,
                     expression -> expression.accept(expressionVisitor, null));
         } else {

src/site/sphinx/usage.rst

@@ -625,7 +625,18 @@ read-only, but its entries are the original mutable AST objects:
 returns their SQL text. Existing ``ColumnSetDefault`` constructors still accept
 opaque strings, for which ``getDefaultExpression()`` returns ``null``.
 Replacing an expression also replaces any opaque value. Unrelated actions
-return an empty list.
+return an empty list. This lookup follows the action's current rendering path:
+changing an operation or retaining unused metadata does not make a fixed-body
+action expose ``SET DEFAULT`` entries it will not render.
+
+``hasActiveColumnDefinitions()`` reports whether the action currently renders
+its column definitions through the general ALTER body. ``getColDataTypeList()``
+continues to expose stored metadata even when another body takes precedence.
+``AlterDeParser`` uses the active path, so expression visitors rewrite the
+selected default or column expressions without rendering inactive metadata.
+Custom ``AlterExpression`` subclasses overriding ``appendBody`` should also
+override ``usesColumnActionBody()`` and ``hasActiveColumnDefinitions()`` when
+they change those dispatch rules.
 
 Structured column attributes
 ============================