Better assignment

src/Storages/IndicesDescription.cpp

@@ -36,6 +36,9 @@ IndexDescription::IndexDescription(const IndexDescription & other)
 
 IndexDescription & IndexDescription::operator=(const IndexDescription & other)
 {
+    if (&other == this)
+        return *this;
+
     if (other.definition_ast)
         definition_ast = other.definition_ast->clone();
     else

src/Storages/KeyDescription.cpp

@@ -22,6 +22,9 @@ KeyDescription::KeyDescription(const KeyDescription & other)
 
 KeyDescription & KeyDescription::operator=(const KeyDescription & other)
 {
+    if (&other == this)
+        return *this;
+
     if (other.definition_ast)
         definition_ast = other.definition_ast->clone();
     else

src/Storages/SelectQueryDescription.cpp

@@ -24,6 +24,9 @@ SelectQueryDescription::SelectQueryDescription(const SelectQueryDescription & ot
 
 SelectQueryDescription & SelectQueryDescription::SelectQueryDescription::operator=(const SelectQueryDescription & other)
 {
+    if (&other == this)
+        return *this;
+
     select_table_id = other.select_table_id;
     if (other.select_query)
         select_query = other.select_query->clone();

src/Storages/StorageInMemoryMetadata.cpp

@@ -30,6 +30,9 @@ StorageInMemoryMetadata::StorageInMemoryMetadata(const StorageInMemoryMetadata &
 
 StorageInMemoryMetadata & StorageInMemoryMetadata::operator=(const StorageInMemoryMetadata & other)
 {
+    if (&other == this)
+        return *this;
+
     columns = other.columns;
     secondary_indices = other.secondary_indices;
     constraints = other.constraints;

src/Storages/TTLDescription.cpp

@@ -72,6 +72,9 @@ TTLDescription::TTLDescription(const TTLDescription & other)
 
 TTLDescription & TTLDescription::operator=(const TTLDescription & other)
 {
+    if (&other == this)
+        return *this;
+
     mode = other.mode;
     if (other.expression_ast)
         expression_ast = other.expression_ast->clone();