Add missing 28 to AppenderParams array impl (#614)

And document appender alternatives for wide tables.

Fixes #367

Author: mlafeldt

crates/duckdb/src/appender/mod.rs

@@ -21,6 +21,41 @@ use crate::{
 /// If you need to share an `Appender` across threads, wrap it in a `Mutex`.
 ///
 /// See [DuckDB concurrency documentation](https://duckdb.org/docs/stable/connect/concurrency.html) for more details.
+///
+/// # Wide Tables (Many Columns)
+///
+/// Array literals `[value; N]` are supported for tables with up to 32 columns.
+///
+/// ```rust,ignore
+/// appender.append_row([0; 32])?;
+/// appender.append_row([1, 2, 3, 4, 5])?;
+/// ```
+///
+/// For tables with more than 32 columns, use one of these alternatives:
+///
+/// ## 1. Slice approach - convert values to `&dyn ToSql`
+///
+/// ```rust,ignore
+/// let values: Vec<i32> = vec![0; 100];
+/// let params: Vec<&dyn ToSql> = values.iter().map(|v| v as &dyn ToSql).collect();
+/// appender.append_row(params.as_slice())?;
+/// ```
+///
+/// ## 2. `params!` macro - write values explicitly
+///
+/// ```rust,ignore
+/// appender.append_row(params![v1, v2, v3, ..., v50])?;
+/// ```
+///
+/// ## 3. `appender_params_from_iter` - pass an iterator directly
+///
+/// ```rust,ignore
+/// use duckdb::appender_params_from_iter;
+/// let values: Vec<i32> = vec![0; 100];
+/// appender.append_row(appender_params_from_iter(values))?;
+/// ```
+///
+/// All three methods can be used interchangeably and mixed in the same appender.
 pub struct Appender<'conn> {
     conn: &'conn Connection,
     app: ffi::duckdb_appender,

crates/duckdb/src/appender_params.rs

@@ -172,9 +172,14 @@ macro_rules! impl_for_array_ref {
 // Following libstd/libcore's (old) lead, implement this for arrays up to `[_;
 // 32]`. Note `[_; 0]` is intentionally omitted for coherence reasons, see the
 // note above the impl of `[&dyn ToSql; 0]` for more information.
+//
+// For tables with more than 32 columns, users should use:
+// - `&[&dyn ToSql]` for dynamic parameter binding (recommended)
+// - `params!` macro
+// - `appender_params_from_iter`
 impl_for_array_ref!(
     1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
-    18 19 20 21 22 23 24 25 26 27 29 30 31 32
+    18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
 );
 
 /// Adapter type which allows any iterator over [`ToSql`] values to implement