docs: Add more examples to updating rows (#1499)

Author: kyleconroy

docs/howto/update.md

@@ -5,12 +5,53 @@ CREATE TABLE authors (
   id         SERIAL PRIMARY KEY,
   bio        text   NOT NULL
 );
+```
 
--- name: UpdateAuthor :exec
-UPDATE authors SET bio = $2
-WHERE id = $1;
+## Single parameter
+
+If your query has a single parameter, your Go method will also have a single
+parameter.
+
+```sql
+-- name: UpdateAuthorBios :exec
+UPDATE authors SET bio = $1;
+```
+
+```go
+package db
+
+import (
+	"context"
+	"database/sql"
+)
+
+type DBTX interface {
+	ExecContext(context.Context, string, ...interface{}) error
+}
+
+func New(db DBTX) *Queries {
+	return &Queries{db: db}
+}
+
+type Queries struct {
+	db DBTX
+}
+
+const updateAuthorBios = `-- name: UpdateAuthorBios :exec
+UPDATE authors SET bio = $1
+`
+
+func (q *Queries) UpdateAuthorBios(ctx context.Context, bio string) error {
+	_, err := q.db.ExecContext(ctx, updateAuthorBios, bio)
+	return err
+}
 ```
 
+## Multiple parameters
+
+If your query has more than one parameter, your Go method will accept a
+`Params` struct.
+
 ```go
 package db
 
@@ -36,8 +77,14 @@ UPDATE authors SET bio = $2
 WHERE id = $1
 `
 
-func (q *Queries) UpdateAuthor(ctx context.Context, id int, bio string) error {
-	_, err := q.db.ExecContext(ctx, updateAuthor, id, bio)
+type UpdateAuthorParams struct {
+	ID  int32
+	Bio string
+}
+
+func (q *Queries) UpdateAuthor(ctx context.Context, arg UpdateAuthorParams) error {
+	_, err := q.db.ExecContext(ctx, updateAuthor, arg.ID, arg.Bio)
 	return err
 }
 ```
+