Constant UNIQUE 

pub const UNIQUE: ColumnMarker;

Adds a UNIQUE constraint to a column, table, or index.

Examples

#[column(unique)]
email: String,

#[SQLiteTable(unique(columns(email, tenant_id)))]
struct Users {
    email: String,
    tenant_id: i32,
}

#[SQLiteIndex(unique)]
struct UsersEmailIdx(Users::email);

See: https://sqlite.org/lang_createtable.html#unique_constraints