Name and type parameters

Bind values through typed method arguments instead of building SQL strings. Use inferred parameter names for direct column comparisons and a sgl.param directive when the application needs a more descriptive name.

Write placeholders and name their role

In a configured SQLite project, ordinary ? placeholders take names and types from the compared columns:

-- sgl.query(FindSailings, many)
SELECT id, origin, destination, departs, seats_free
FROM sailings
WHERE origin = ? AND destination = ?
ORDER BY departs;

Name range bounds explicitly when that makes the caller clearer:

-- sgl.query(SailingsDeparting, many)
-- ?1 as sgl.param(earliest)
-- ?2 as sgl.param(latest)
SELECT id, origin, destination, departs, seats_free
FROM sailings
WHERE departs >= ?1 AND departs < ?2
ORDER BY departs;

A single parameter normally becomes one typed method argument. Several parameters produce a query-specific params struct. The schema declares the columns supplying these types.

Pass the generated params struct

Run sgl generate and construct store.New(database). Fill the inferred fields:

	route, err := queries.FindSailings(ctx, store.FindSailingsParams{
		Origin:      "Penzance",
		Destination: "St Mary's",
	})
	if err != nil {
		return fmt.Errorf("finding sailings: %w", err)
	}

For the named range parameters, use the directive’s names:

	midday, err := queries.SailingsDeparting(ctx, store.SailingsDepartingParams{
		Earliest: "10:00",
		Latest:   "15:00",
	})
	if err != nil {
		return fmt.Errorf("finding midday sailings: %w", err)
	}

Use a parameter’s type: quality or an SQL cast when the expression provides no useful type. Keep values out of the SQL string.

Check names and bound values

From the Seagull repository root, run the parameter example:

cd examples/sqlite/003_parameters
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:

Penzance to St Mary's:
  sailing 1 at 09:15, 40 seats free
  sailing 3 at 14:30, 4 seats free
Departing between 10:00 and 15:00:
  sailing 2 at 11:00, St Mary's to Tresco
  sailing 3 at 14:30, Penzance to St Mary's
booked 3 seats on sailing 3
sailing 3 has fewer than 3 seats free

Use the dialect’s placeholder forms

Placeholder spelling follows the dialect: $N on PostgreSQL, ? or ?N on SQLite, ? on MySQL and typed {name:Type} on ClickHouse. A repeated named placeholder is one logical input; generation rewrites it to the execution form the driver needs. Use directives for input shape, and SQL for the condition the database should apply.

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.