The SQL client can trace query execution when Vert.x has tracing enabled.

The client reports the following _client_ spans:

- `Query` operation name
- tags
  - `db.user`: the database username
  - `db.instance`: the database instance
  - `db.statement`: the SQL query
  - `db.type`: _sql_

The default tracing policy is {@link io.vertx.core.tracing.TracingPolicy#PROPAGATE}, the client
will only create a span when involved in an active trace.

You can change the client policy with {@link io.vertx.sqlclient.SqlConnectOptions#setTracingPolicy},
e.g you can set {@link io.vertx.core.tracing.TracingPolicy#ALWAYS} to always report
a span:

[source,$lang]
----
{@link examples.SqlClientExamples#tracing01}
----
