> ## Documentation Index
> Fetch the complete documentation index at: https://private-7c7dfe99-revert-104359-revert-104251-parquet-single.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

> Documentation for Manipulating Key Expressions

# ALTER TABLE ... MODIFY ORDER BY

```sql theme={null}
ALTER TABLE [db].name [ON CLUSTER cluster] MODIFY ORDER BY new_expression
```

The command changes the [sorting key](/reference/engines/table-engines/mergetree-family/mergetree) of the table to `new_expression` (an expression or a tuple of expressions). Primary key remains the same.

The command is lightweight in a sense that it only changes metadata. To keep the property that data part rows are ordered by the sorting key expression you cannot add expressions containing existing columns to the sorting key (only columns added by the `ADD COLUMN` command in the same `ALTER` query, without default column value).

For the same reason you cannot change the sort direction (`ASC` or `DESC`) of a sorting key column that `new_expression` keeps: the existing parts stay physically sorted in the direction the column had when they were written, and no regular data part records that direction. To use a different direction, create a new table with the desired `ORDER BY` and copy the data into it with `INSERT ... SELECT`.

<Note>
  It only works for tables in the [`MergeTree`](/reference/engines/table-engines/mergetree-family/mergetree) family (including [replicated](/reference/engines/table-engines/mergetree-family/replication) tables).
</Note>

**Part of:** `ALTER`

**Related:** `ALTER`, `CREATE TABLE`, `ALTER TABLE ... MODIFY SAMPLE BY`