Add optional filters

Let a caller omit individual filters by passing nil. Declare the Go parameter optional and write SQL that explicitly disables the condition when its parameter is NULL.

Declare each optional predicate

In a configured project, add the optional bindings and their NULL tests to the query header and predicate:

-- sgl.query(SearchTrips, many)
-- ?1 as sgl.param(destination, optional: true)
-- ?2 as sgl.param(max_price, optional: true)
-- ?3 as sgl.param(dogs_welcome, optional: true)
SELECT id, name, destination, price_pence, dogs_welcome
FROM trips
WHERE (?1 IS NULL OR destination = ?1)
  AND (?2 IS NULL OR price_pence <= ?2)
  AND (?3 IS NULL OR dogs_welcome = ?3)
ORDER BY price_pence, id;

The pointer controls whether a value is present; the IS NULL OR expression controls whether the SQL filter applies. Keep both parts when adapting this pattern to another column.

Pass nil or a pointer to the desired value

Run sgl generate and construct store.New(database). An empty SearchTripsParams applies no filters; a non-nil field applies that filter. The caller exercises each choice:

	searches := []struct {
		label      string
		parameters store.SearchTripsParams
	}{
		{label: "no filters", parameters: store.SearchTripsParams{}},
		{label: "to Gull Rock", parameters: store.SearchTripsParams{Destination: new("Gull Rock")}},
		{label: "£15 or less", parameters: store.SearchTripsParams{MaxPrice: new(int64(1500))}},
		{label: "to Gull Rock with a dog", parameters: store.SearchTripsParams{Destination: new("Gull Rock"), DogsWelcome: new(true)}},
	}

Pass the chosen params to queries.SearchTrips(ctx, params) and handle its error before reading the returned rows.

Check omitted and combined filters

From the Seagull repository root, run the optional-filter example:

cd examples/sqlite/011_optional_filters
go test .

The example test provides its local inputs. See its caller for the exact Go API and its test for assertions and failure handling.

The complete example produces:

no filters:              Sunset sail, Seal spotting, Mackerel fishing, Puffin cruise
to Gull Rock:            Seal spotting, Mackerel fishing
£15 or less:             Sunset sail, Seal spotting
to Gull Rock with a dog: Seal spotting

Keep the SQL NULL test explicit

On PostgreSQL, cast a parameter first encountered in IS NULL, for example $1::text IS NULL, so the server can type it. On ClickHouse use a nullable placeholder type, such as {destination:Nullable(String)}. optional: true shapes the Go input but never removes or rewrites the SQL predicate, and cannot be combined with default:.

See the directives reference for the complete contract. The example browser exposes other engine variants; use their actual SQL rather than changing only the dialect name.