fix(mysql): show inherited charset and collation in structure editor

crates/dbx-core/src/table_structure_sql/column_format.rs

@@ -1,7 +1,41 @@
 use super::dialect::{is_oracle_like, StructureDialect};
-use super::types::EditableStructureColumn;
+use super::types::{EditableStructureColumn, TableStructureSqlOptions};
 use super::util::{clean, format_default_for_sql, normalize_default, quote_ident, quote_string};
 
+/// Drops the `CHARACTER SET` / `COLLATE` inputs of MySQL columns that merely
+/// inherit the table's default collation, so the generated DDL does not spell
+/// out clauses the server would apply anyway.
+///
+/// MySQL reports the *effective* collation of every character column and never
+/// records whether it was written out explicitly, so "equals the table default"
+/// is the only signal available. Omitting the clauses is equivalent to keeping
+/// them: a column definition without `CHARACTER SET` takes the table default,
+/// which is exactly the value being dropped here. This runs on the DDL inputs
+/// only — introspection (`get_columns`) still reports the real values so the
+/// structure editor can show the column's current charset and collation.
+///
+/// The original snapshot is normalized alongside the draft so that an untouched
+/// column does not register as a charset change and trigger a needless `MODIFY`.
+pub(super) fn strip_inherited_mysql_column_charsets(options: &mut TableStructureSqlOptions) {
+    let Some(table_collation) = options.table_collation.as_deref().map(str::trim).filter(|value| !value.is_empty())
+    else {
+        return;
+    };
+    let inherits = |collation: &str| collation.trim().eq_ignore_ascii_case(table_collation);
+    for column in &mut options.columns {
+        if inherits(&column.collation) {
+            column.character_set = String::new();
+            column.collation = String::new();
+        }
+        if let Some(original) = column.original.as_mut() {
+            if original.collation.as_deref().is_some_and(inherits) {
+                original.character_set = None;
+                original.collation = None;
+            }
+        }
+    }
+}
+
 pub(super) fn column_definition(dialect: StructureDialect, column: &EditableStructureColumn) -> String {
     let data_type = column_data_type(dialect, column);
     let mut parts = vec![quote_ident(dialect, &column.name), data_type];

crates/dbx-core/src/table_structure_sql/create_table.rs

@@ -1,6 +1,6 @@
 use super::column_format::{
     column_data_type, column_extra_clause, has_dameng_identity, is_dameng_identity_compatible_type,
-    is_mysql_character_data_type, is_mysql_timestamp_type,
+    is_mysql_character_data_type, is_mysql_timestamp_type, strip_inherited_mysql_column_charsets,
 };
 use super::comments::{build_sqlserver_column_comment_sql, build_sqlserver_table_comment_sql};
 use super::dialect::{capabilities_for, database_label, StructureDialect};
@@ -26,6 +26,7 @@ pub fn build_create_table_sql(mut options: TableStructureSqlOptions) -> TableStr
         dialect = capabilities.dialect;
     }
     options.table_name = clean(&options.table_name);
+    strip_inherited_mysql_column_charsets(&mut options);
     let mut warnings = Vec::new();
     warnings.extend(validate_mysql_engine(&options));
     // Fail closed: a concurrent-index request on a partitioned parent (or on an

crates/dbx-core/src/table_structure_sql/sqlite_rebuild.rs

@@ -1519,6 +1519,7 @@ mod tests {
             mysql_engine: None,
             partitioned: false,
             is_gaussdb_m_mode: false,
+            table_collation: None,
         }
     }
 

crates/dbx-core/src/table_structure_sql/types.rs

@@ -216,6 +216,14 @@ pub struct TableStructureSqlOptions {
     pub original_table_comment: Option<String>,
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub mysql_engine: Option<String>,
+    /// MySQL only: the table's current default collation
+    /// (`information_schema.TABLES.TABLE_COLLATION`). A column whose collation
+    /// merely matches it inherits the table default, so its `CHARACTER SET` /
+    /// `COLLATE` clauses are redundant and are dropped from the generated DDL.
+    /// Introspection keeps reporting the column's real values, which is what
+    /// the structure editor renders in its charset/collation pickers.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub table_collation: Option<String>,
     /// Whether the target table is a partitioned parent table (PostgreSQL
     /// `relkind = 'p'`). PostgreSQL rejects `CREATE INDEX CONCURRENTLY` on
     /// partitioned parents, so the builder refuses such a request up front