# ALTER TABLE SET TYPE

ALTER TABLE SET TYPE SQL keyword reference documentation.

Converts a non-WAL table to WAL, or a WAL table to non-WAL.

:::info

**Upgrading QuestDB?**

Apply table conversions separately from the version upgrade.

If upgrading, match the following sequence:

1. Convert/`ALTER` tables
2. Restart
3. Upgrade
4. Restart

:::

## Syntax

```questdb-sql
ALTER TABLE tableName SET TYPE [BYPASS] WAL;
```

## Description

The command schedules the conversion of the specified table to WAL or non-WAL
type. The actual conversion takes place on the next restart of the server.

If the command issued more than once before the restart, the last command
overrides all previous ones.

If the target type of the conversion is the same as the current type of the
table, the conversion request is ignored.

## Examples

To convert a non-WAL table to WAL:

```sql
ALTER TABLE weather SET TYPE WAL;
-- now restart instance
```

To convert a WAL table to non-WAL:

```sql
ALTER TABLE weather SET TYPE BYPASS WAL;
-- now restart instance
```