I'd like to create index for PostGIS db in Postgresql.

This is my table (simplified):

```
CREATE EXTENSION postgis;
CREATE EXTENSION btree_gist;
CREATE TABLE table1 (id int, data boolean);
SELECT AddGeometryColumn('table1', 'geom', 900913, 'linestring', 2);

```

When I create the index:

```
CREATE INDEX index1 ON table1 USING gist(data, geom);

```

it failed with error message:

```
ERROR:  data type boolean has no default operator class for access method "gist"
HINT: You must specify an operator class for the index or define a default operator class for the data type.

```

The problem is btree\_gist doesn't support `boolean` type. It did work with other types like `int`.

But I cannot change the type from `boolean` to `int` because above is simplified. In my original issue, what I want is index on expression and I cannot modify the (program generated) expression.