drizzle_core/sql/

mod.rs

mod chunk;
mod comment;
mod cte;
mod owned;
mod tokens;

use crate::prelude::*;
use crate::{
    param::{Param, ParamBind},
    placeholder::Placeholder,
    traits::{SQLParam, ToSQL},
};
pub use chunk::*;
pub use comment::{comment, comment_tags};
use core::fmt::{Display, Write};
pub use owned::*;
use smallvec::SmallVec;
pub use tokens::*;

#[cfg(feature = "profiling")]
use crate::profile_sql;

/// SQL fragment builder with flat chunk storage.
///
/// Uses `SmallVec<[SQLChunk; 8]>` for inline storage of typical SQL fragments
/// without heap allocation.
#[derive(Debug, Clone)]
pub struct SQL<'a, V: SQLParam> {
    pub chunks: SmallVec<[SQLChunk<'a, V>; 8]>,
}

impl<'a, V: SQLParam> SQL<'a, V> {
    const POSITIONAL_PLACEHOLDER: Placeholder = Placeholder::anonymous();

    // ==================== constructors ====================

    /// Creates an empty SQL fragment
    #[inline]
    #[must_use]
    pub const fn empty() -> Self {
        Self {
            chunks: SmallVec::new_const(),
        }
    }

    // ==================== constructors ====================

    /// Creates SQL with a single token
    #[inline]
    #[must_use]
    pub fn token(t: Token) -> Self {
        Self {
            chunks: smallvec::smallvec![SQLChunk::Token(t)],
        }
    }

    /// Creates an empty SQL fragment with pre-allocated chunk capacity.
    #[inline]
    #[must_use]
    pub fn with_capacity_chunks(capacity: usize) -> Self {
        Self {
            chunks: SmallVec::with_capacity(capacity),
        }
    }

    /// Creates SQL with a quoted identifier
    #[inline]
    pub fn ident(name: impl Into<Cow<'a, str>>) -> Self {
        Self {
            chunks: smallvec::smallvec![SQLChunk::Ident(name.into())],
        }
    }

    /// Creates a comma-separated list of unqualified column identifiers.
    #[must_use]
    pub fn columns(columns: &[ColumnRef]) -> Self {
        let mut sql = Self::with_capacity_chunks(columns.len().saturating_mul(2));
        for (index, column) in columns.iter().enumerate() {
            if index > 0 {
                sql.push_mut(Token::COMMA);
            }
            sql.append_mut(Self::ident(column.name));
        }
        sql
    }

    /// Creates SQL with raw text (unquoted)
    #[inline]
    pub fn raw(text: impl Into<Cow<'a, str>>) -> Self {
        Self {
            chunks: smallvec::smallvec![SQLChunk::Raw(text.into())],
        }
    }

    /// Creates SQL with a single unsigned integer literal.
    #[inline]
    #[must_use]
    pub fn number(value: usize) -> Self {
        Self {
            chunks: smallvec::smallvec![SQLChunk::Number(value)],
        }
    }

    /// Creates SQL with a single parameter value
    #[inline]
    pub fn param(value: impl Into<Cow<'a, V>>) -> Self {
        Self {
            chunks: smallvec::smallvec![SQLChunk::Param(Param {
                value: Some(value.into()),
                placeholder: Self::POSITIONAL_PLACEHOLDER,
            })],
        }
    }

    /// Creates SQL with a binary parameter value (BLOB/bytea)
    ///
    /// Prefer this over `SQL::param(Vec<u8>)` to avoid list semantics.
    #[inline]
    pub fn bytes(bytes: impl Into<Cow<'a, [u8]>>) -> Self
    where
        V: From<&'a [u8]> + From<Vec<u8>> + Into<Cow<'a, V>>,
    {
        match bytes.into() {
            Cow::Borrowed(value) => Self::param(V::from(value)),
            Cow::Owned(value) => Self::param(V::from(value)),
        }
    }

    /// Creates SQL referencing a table
    #[inline]
    #[must_use]
    pub fn table(table: TableRef) -> Self {
        Self {
            chunks: smallvec::smallvec![SQLChunk::Table(TableSqlRef::from_table_ref(table))],
        }
    }

    /// Creates SQL referencing a column
    #[inline]
    #[must_use]
    pub fn column(column: ColumnRef) -> Self {
        Self {
            chunks: smallvec::smallvec![SQLChunk::Column(ColumnSqlRef::from_column_ref(column))],
        }
    }

    /// Creates SQL for a function call: NAME(args)
    /// Subqueries are automatically wrapped in parentheses: NAME((SELECT ...))
    #[inline]
    pub fn func(name: &'static str, args: Self) -> Self {
        let args = args.parens_if_subquery();
        SQL::raw(name)
            .push(Token::LPAREN)
            .append(args)
            .push(Token::RPAREN)
    }

    // ==================== builder methods ====================

    /// Append another SQL fragment (flat extend)
    #[inline]
    #[must_use]
    pub fn append(mut self, other: impl Into<Self>) -> Self {
        #[cfg(feature = "profiling")]
        profile_sql!("append");
        let other = other.into();

        if self.chunks.is_empty() {
            return other;
        }
        if other.chunks.is_empty() {
            return self;
        }

        self.chunks.extend(other.chunks);
        self
    }

    #[inline]
    pub fn append_mut(&mut self, other: impl Into<Self>) {
        #[cfg(feature = "profiling")]
        profile_sql!("append_mut");
        let other = other.into();

        if self.chunks.is_empty() {
            self.chunks = other.chunks;
            return;
        }
        if other.chunks.is_empty() {
            return;
        }

        self.chunks.extend(other.chunks);
    }

    /// Push a single chunk
    #[inline]
    #[must_use]
    pub fn push(mut self, chunk: impl Into<SQLChunk<'a, V>>) -> Self {
        self.chunks.push(chunk.into());
        self
    }

    #[inline]
    pub fn push_mut(&mut self, chunk: impl Into<SQLChunk<'a, V>>) {
        self.chunks.push(chunk.into());
    }

    /// Pre-allocates capacity for additional chunks
    #[inline]
    #[must_use]
    pub fn with_capacity(mut self, additional: usize) -> Self {
        self.chunks.reserve(additional);
        self
    }

    // ==================== combinators ====================

    /// Joins multiple SQL fragments with a separator
    pub fn join<T>(sqls: T, separator: Token) -> Self
    where
        T: IntoIterator,
        T::Item: ToSQL<'a, V>,
    {
        #[cfg(feature = "profiling")]
        profile_sql!("join");

        let mut iter = sqls.into_iter();
        let Some(first) = iter.next() else {
            return SQL::empty();
        };

        let mut result = first.into_sql();
        let (lower, upper) = iter.size_hint();
        if let Some(upper) = upper {
            result.chunks.reserve(upper.saturating_mul(2));
        } else if lower > 0 {
            result.chunks.reserve(lower * 2);
        }

        for item in iter {
            result.chunks.push(SQLChunk::Token(separator));
            let other = item.into_sql();
            if !other.chunks.is_empty() {
                result.chunks.extend(other.chunks);
            }
        }
        result
    }

    /// Wrap in parentheses: (self)
    #[inline]
    #[must_use]
    pub fn parens(self) -> Self {
        SQL::token(Token::LPAREN).append(self).push(Token::RPAREN)
    }

    /// Wrap this SQL fragment in parentheses only when it is a subquery.
    #[inline]
    #[must_use]
    pub fn parens_if_subquery(self) -> Self {
        if self.is_subquery() {
            self.parens()
        } else {
            self
        }
    }

    /// Check if this SQL fragment is a subquery (starts with SELECT/WITH).
    #[inline]
    pub fn is_subquery(&self) -> bool {
        matches!(
            self.chunks.first(),
            Some(SQLChunk::Token(Token::SELECT | Token::WITH))
        )
    }

    /// Creates an aliased version: self AS "name"
    #[inline]
    #[must_use]
    pub fn alias(self, name: impl Into<Cow<'a, str>>) -> Self {
        self.push(Token::AS).push(SQLChunk::Ident(name.into()))
    }

    /// Creates a comma-separated list of parameters.
    /// Builds chunks directly without intermediate SQL allocations.
    #[inline]
    pub fn param_list<I>(values: I) -> Self
    where
        I: IntoIterator,
        I::Item: Into<Cow<'a, V>>,
    {
        let iter = values.into_iter();
        let (lower, upper) = iter.size_hint();
        let count = upper.unwrap_or(lower);
        let mut chunks = SmallVec::with_capacity(count.saturating_mul(2).saturating_sub(1));
        for (i, v) in iter.enumerate() {
            if i > 0 {
                chunks.push(SQLChunk::Token(Token::COMMA));
            }
            chunks.push(SQLChunk::Param(Param {
                value: Some(v.into()),
                placeholder: Self::POSITIONAL_PLACEHOLDER,
            }));
        }
        SQL { chunks }
    }

    /// Creates a comma-separated list of column assignments: "col" = ?
    /// Builds chunks directly without intermediate SQL allocations.
    #[inline]
    pub fn assignments<I, T>(pairs: I) -> Self
    where
        I: IntoIterator<Item = (&'static str, T)>,
        T: Into<Cow<'a, V>>,
    {
        let iter = pairs.into_iter();
        let (lower, upper) = iter.size_hint();
        let count = upper.unwrap_or(lower);
        // Each assignment: Ident + EQ + Param = 3 chunks, plus commas
        let mut chunks = SmallVec::with_capacity(count.saturating_mul(4).saturating_sub(1));
        for (i, (col, val)) in iter.enumerate() {
            if i > 0 {
                chunks.push(SQLChunk::Token(Token::COMMA));
            }
            chunks.push(SQLChunk::Ident(Cow::Borrowed(col)));
            chunks.push(SQLChunk::Token(Token::EQ));
            chunks.push(SQLChunk::Param(Param {
                value: Some(val.into()),
                placeholder: Self::POSITIONAL_PLACEHOLDER,
            }));
        }
        SQL { chunks }
    }

    /// Creates comma-separated column assignments from pre-built SQL fragments,
    /// such as `"col" = <expression>`.
    ///
    /// Unlike `assignments()` which wraps each value in `SQL::param()`, this variant
    /// accepts pre-built `SQL` fragments, preserving placeholders and raw expressions.
    /// Builds chunks directly without intermediate SQL allocations.
    #[inline]
    pub fn assignments_sql<I>(pairs: I) -> Self
    where
        I: IntoIterator<Item = (&'static str, Self)>,
    {
        let iter = pairs.into_iter();
        let (lower, upper) = iter.size_hint();
        let count = upper.unwrap_or(lower);
        let mut chunks = SmallVec::with_capacity(count.saturating_mul(4).saturating_sub(1));
        for (i, (col, sql)) in iter.enumerate() {
            if i > 0 {
                chunks.push(SQLChunk::Token(Token::COMMA));
            }
            chunks.push(SQLChunk::Ident(Cow::Borrowed(col)));
            chunks.push(SQLChunk::Token(Token::EQ));
            chunks.extend(sql.chunks);
        }
        SQL { chunks }
    }

    // ==================== output methods ====================

    /// Maps parameter values from type `V` to type `U` using the provided function.
    ///
    /// Only `Param` chunks are affected; all other chunks pass through unchanged.
    /// This is useful for converting between owned and borrowed value types
    /// (e.g. `OwnedPostgresValue` → `PostgresValue<'a>`).
    pub fn map_params<U: SQLParam>(self, mut f: impl FnMut(V) -> U) -> SQL<'a, U> {
        let chunks = self
            .chunks
            .into_iter()
            .map(|chunk| match chunk {
                SQLChunk::Token(t) => SQLChunk::Token(t),
                SQLChunk::Ident(s) => SQLChunk::Ident(s),
                SQLChunk::Raw(s) => SQLChunk::Raw(s),
                SQLChunk::Number(n) => SQLChunk::Number(n),
                SQLChunk::Param(param) => SQLChunk::Param(Param::new(
                    param.placeholder,
                    param.value.map(|cow| Cow::Owned(f(cow.into_owned()))),
                )),
                SQLChunk::Table(t) => SQLChunk::Table(t),
                SQLChunk::Column(c) => SQLChunk::Column(c),
            })
            .collect();
        SQL { chunks }
    }

    /// Own every borrowed SQL fragment while mapping parameter values.
    ///
    /// This is used by generated models that outlive their source values. It
    /// preserves identifiers, raw fragments, placeholders, tables, and columns
    /// instead of assuming the fragment consists of a single parameter.
    pub fn into_owned_with<U: SQLParam>(self, mut f: impl FnMut(V) -> U) -> SQL<'static, U> {
        let chunks = self
            .chunks
            .into_iter()
            .map(|chunk| match chunk {
                SQLChunk::Token(token) => SQLChunk::Token(token),
                SQLChunk::Ident(value) => SQLChunk::Ident(Cow::Owned(value.into_owned())),
                SQLChunk::Raw(value) => SQLChunk::Raw(Cow::Owned(value.into_owned())),
                SQLChunk::Number(value) => SQLChunk::Number(value),
                SQLChunk::Param(param) => SQLChunk::Param(Param::new(
                    param.placeholder,
                    param.value.map(|value| Cow::Owned(f(value.into_owned()))),
                )),
                SQLChunk::Table(table) => SQLChunk::Table(table),
                SQLChunk::Column(column) => SQLChunk::Column(column),
            })
            .collect();
        SQL { chunks }
    }

    /// Converts to owned version (consuming self to avoid clone)
    #[inline]
    pub fn into_owned(self) -> OwnedSQL<V> {
        OwnedSQL::from(self)
    }

    /// Returns the SQL string with dialect-appropriate placeholders.
    /// Uses `$1, $2, ...` for `PostgreSQL`, `:name` or `?` for `SQLite`, `?` for `MySQL`.
    pub fn sql(&self) -> String {
        #[cfg(feature = "profiling")]
        profile_sql!("sql");
        #[cfg(feature = "profiling")]
        crate::drizzle_profile_scope!("sql_render", "sql.estimate");
        let (sql_cap, _) = self.render_capacity_estimate();
        let mut buf = String::with_capacity(sql_cap);
        self.write_to(&mut buf);
        buf
    }

    /// Whether this statement has a `RETURNING` clause (outside any
    /// parentheses), so it returns rows although it changes data.
    #[must_use]
    pub fn has_returning(&self) -> bool {
        let mut depth = 0usize;
        for chunk in &self.chunks {
            match chunk {
                SQLChunk::Token(Token::LPAREN) => depth += 1,
                SQLChunk::Token(Token::RPAREN) => depth = depth.saturating_sub(1),
                SQLChunk::Token(Token::RETURNING) if depth == 0 => return true,
                _ => {}
            }
        }
        false
    }

    /// Returns the SQL string with every bound value written as a literal
    /// instead of a placeholder, for statements that cannot take parameters,
    /// such as the body of a `CREATE VIEW`.
    ///
    /// Returns `None` when a placeholder has no bound value, or a value has
    /// no literal form in this dialect (see [`SQLParam::write_literal`]).
    #[must_use]
    pub fn inline_sql(&self) -> Option<String> {
        let (sql_cap, _) = self.render_capacity_estimate();
        let mut buf = String::with_capacity(sql_cap);
        for (i, chunk) in self.chunks.iter().enumerate() {
            match chunk {
                SQLChunk::Param(param) => {
                    let value = param.value.as_ref()?;
                    if !value.as_ref().write_literal(&mut buf) {
                        return None;
                    }
                }
                _ => chunk.write(&mut buf),
            }

            if self.ends_select_head(i) {
                self.write_select_columns(&mut buf, i);
            }

            if self.needs_space(i) {
                buf.push(' ');
            }
        }
        Some(buf)
    }

    /// Generates the SQL string and collects parameter references in a single pass.
    ///
    /// This is the preferred method for driver execution paths since it avoids
    /// iterating the chunk list twice (once for `sql()`, once for `params()`).
    pub fn build(&self) -> (String, SmallVec<[&V; 8]>) {
        self.build_with(crate::dialect::ParamStyle::for_dialect(V::DIALECT))
    }

    /// Same as [`build`](Self::build) but lets the caller override the
    /// placeholder style. Drivers that speak the dialect but bind parameters
    /// differently (e.g. AWS Data API on Postgres) use this to emit
    /// `:1, :2, ...` instead of `$1, $2, ...` without any post-hoc rewriting.
    pub fn build_with(&self, style: crate::dialect::ParamStyle) -> (String, SmallVec<[&V; 8]>) {
        use crate::dialect::Dialect;

        #[cfg(feature = "profiling")]
        crate::drizzle_profile_scope!("sql_render", "build");
        #[cfg(feature = "profiling")]
        crate::drizzle_profile_scope!("sql_render", "build.estimate");
        let (sql_cap, param_cap) = self.render_capacity_estimate();
        let mut buf = String::with_capacity(sql_cap);
        let mut params: SmallVec<[&V; 8]> = SmallVec::with_capacity(param_cap);
        let mut param_index = 1usize;
        let mut sqlite_names = SQLiteNamedParams::default();

        #[cfg(feature = "profiling")]
        crate::drizzle_profile_scope!("sql_render", "build.render");
        for (i, chunk) in self.chunks.iter().enumerate() {
            match chunk {
                SQLChunk::Param(param) => {
                    let mut repeated_name = false;
                    if let Some(name) = param.placeholder.name
                        && V::DIALECT == Dialect::SQLite
                    {
                        let _ = buf.write_char(':');
                        let _ = buf.write_str(name);
                        repeated_name = sqlite_names.is_repeat(name);
                    } else {
                        style.write(param_index, &mut buf);
                    }
                    param_index += 1;
                    // SQLite gives every distinct `:name` one parameter
                    // slot, so a repeated name binds its value only once.
                    if !repeated_name && let Some(value) = &param.value {
                        params.push(value.as_ref());
                    }
                }
                _ => chunk.write(&mut buf),
            }

            if self.ends_select_head(i) {
                self.write_select_columns(&mut buf, i);
            }

            if self.needs_space(i) {
                let _ = buf.write_char(' ');
            }
        }

        (buf, params)
    }

    /// Write SQL to a buffer with dialect-appropriate placeholders.
    /// Uses `$1, $2, ...` for `PostgreSQL`, `?` or `:name` for `SQLite`, `?` for `MySQL`.
    #[inline]
    pub fn write_to(&self, buf: &mut impl core::fmt::Write) {
        self.write_to_with(buf, crate::dialect::ParamStyle::for_dialect(V::DIALECT));
    }

    /// Same as [`write_to`](Self::write_to) but with a caller-chosen
    /// placeholder style.
    pub fn write_to_with(
        &self,
        buf: &mut impl core::fmt::Write,
        style: crate::dialect::ParamStyle,
    ) {
        use crate::dialect::Dialect;

        #[cfg(feature = "profiling")]
        crate::drizzle_profile_scope!("sql_render", "write_to");
        let mut param_index = 1usize;
        for (i, chunk) in self.chunks.iter().enumerate() {
            match chunk {
                SQLChunk::Param(param) => {
                    if let Some(name) = param.placeholder.name
                        && V::DIALECT == Dialect::SQLite
                    {
                        let _ = buf.write_char(':');
                        let _ = buf.write_str(name);
                    } else {
                        style.write(param_index, buf);
                    }
                    param_index += 1;
                }
                _ => chunk.write(buf),
            }

            if self.ends_select_head(i) {
                self.write_select_columns(buf, i);
            }

            if self.needs_space(i) {
                let _ = buf.write_char(' ');
            }
        }
    }

    /// Write a single chunk with pattern detection
    #[inline]
    pub fn write_chunk_to(
        &self,
        buf: &mut impl core::fmt::Write,
        chunk: &SQLChunk<'a, V>,
        index: usize,
    ) {
        chunk.write(buf);
        if self.ends_select_head(index) {
            self.write_select_columns(buf, index);
        }
    }

    /// Whether the chunk at `index` ends a `SELECT` head with no projection,
    /// so the projection must be expanded before the `FROM` that follows.
    ///
    /// The head is `SELECT`, `SELECT DISTINCT`, or `PostgreSQL`'s
    /// `SELECT DISTINCT ON (...)`.
    fn ends_select_head(&self, index: usize) -> bool {
        if !matches!(
            self.chunks.get(index + 1),
            Some(SQLChunk::Token(Token::FROM))
        ) {
            return false;
        }
        let token_at = |position: Option<usize>| match position.and_then(|p| self.chunks.get(p)) {
            Some(SQLChunk::Token(token)) => Some(*token),
            _ => None,
        };

        match self.chunks[index] {
            SQLChunk::Token(Token::SELECT) => true,
            SQLChunk::Token(Token::DISTINCT) => {
                matches!(token_at(index.checked_sub(1)), Some(Token::SELECT))
            }
            SQLChunk::Token(Token::RPAREN) => {
                // Find the `(` this `)` closes, then look for `SELECT DISTINCT ON`.
                let mut depth = 0usize;
                let mut open = None;
                for position in (0..index).rev() {
                    match self.chunks[position] {
                        SQLChunk::Token(Token::RPAREN) => depth += 1,
                        SQLChunk::Token(Token::LPAREN) if depth == 0 => {
                            open = Some(position);
                            break;
                        }
                        SQLChunk::Token(Token::LPAREN) => depth -= 1,
                        _ => {}
                    }
                }
                open.is_some_and(|open| {
                    matches!(token_at(open.checked_sub(1)), Some(Token::ON))
                        && matches!(token_at(open.checked_sub(2)), Some(Token::DISTINCT))
                        && matches!(token_at(open.checked_sub(3)), Some(Token::SELECT))
                })
            }
            _ => false,
        }
    }

    /// Write the projection of a `SELECT` head that ends at `head_end` and
    /// has no explicit column list: every column of the tables in the
    /// following `FROM` clause, or `*` for any other source.
    #[inline]
    pub(crate) fn write_select_columns(&self, buf: &mut impl core::fmt::Write, head_end: usize) {
        let chunks = self.chunks.get(head_end + 1..head_end + 3);
        match chunks {
            Some([SQLChunk::Token(Token::FROM), SQLChunk::Table(_)]) => {
                let _ = buf.write_char(' ');
                let mut first = true;
                let mut depth = 0usize;

                for (index, chunk) in self.chunks.iter().enumerate().skip(head_end + 2) {
                    match chunk {
                        SQLChunk::Token(Token::LPAREN) => depth += 1,
                        SQLChunk::Token(Token::RPAREN) if depth == 0 => break,
                        SQLChunk::Token(Token::RPAREN) => depth -= 1,
                        SQLChunk::Token(
                            Token::WHERE
                            | Token::GROUP
                            | Token::HAVING
                            | Token::ORDER
                            | Token::LIMIT
                            | Token::OFFSET
                            | Token::WINDOW
                            | Token::FOR
                            | Token::UNION
                            | Token::INTERSECT
                            | Token::EXCEPT
                            | Token::SELECT,
                        ) if depth == 0 => break,
                        SQLChunk::Table(table) if depth == 0 => {
                            if !first {
                                let _ = buf.write_str(", ");
                            }
                            let alias = match self.chunks.get(index + 1..index + 3) {
                                Some([SQLChunk::Token(Token::AS), SQLChunk::Ident(alias)]) => {
                                    Some(alias.as_ref())
                                }
                                _ => None,
                            };
                            Self::write_qualified_columns_as(buf, table, alias);
                            first = false;
                        }
                        _ => {}
                    }
                }
            }
            Some([SQLChunk::Token(Token::FROM), _]) => {
                let _ = buf.write_char(' ');
                let _ = buf.write_str(Token::STAR.as_str());
            }
            _ => {}
        }
    }

    /// Write fully qualified columns for a table
    #[inline]
    pub fn write_qualified_columns(buf: &mut impl core::fmt::Write, table: &TableSqlRef) {
        Self::write_qualified_columns_as(buf, table, None);
    }

    #[inline]
    fn write_qualified_columns_as(
        buf: &mut impl core::fmt::Write,
        table: &TableSqlRef,
        alias: Option<&str>,
    ) {
        if table.column_names.is_empty() {
            if let Some(alias) = alias {
                chunk::write_dialect_quoted_ident(V::DIALECT, buf, alias);
            } else {
                if let Some(schema) = table.schema {
                    chunk::write_dialect_quoted_ident(V::DIALECT, buf, schema);
                    let _ = buf.write_char('.');
                }
                chunk::write_dialect_quoted_ident(V::DIALECT, buf, table.name);
            }
            let _ = buf.write_str(".*");
            return;
        }

        for (i, col_name) in table.column_names.iter().enumerate() {
            if i > 0 {
                let _ = buf.write_str(", ");
            }
            if let Some(alias) = alias {
                chunk::write_dialect_quoted_ident(V::DIALECT, buf, alias);
            } else {
                if let Some(schema) = table.schema {
                    chunk::write_dialect_quoted_ident(V::DIALECT, buf, schema);
                    let _ = buf.write_char('.');
                }
                chunk::write_dialect_quoted_ident(V::DIALECT, buf, table.name);
            }
            let _ = buf.write_char('.');
            chunk::write_dialect_quoted_ident(V::DIALECT, buf, col_name);
        }
    }

    /// Simplified spacing logic
    #[inline]
    fn needs_space(&self, index: usize) -> bool {
        let Some(next) = self.chunks.get(index + 1) else {
            return false;
        };

        let current = &self.chunks[index];
        chunk_needs_space(current, next)
    }

    #[inline]
    fn render_capacity_estimate(&self) -> (usize, usize) {
        let mut sql_cap = 0usize;
        let mut param_cap = 0usize;

        for chunk in &self.chunks {
            sql_cap = sql_cap.saturating_add(match chunk {
                SQLChunk::Ident(_) | SQLChunk::Raw(_) => 20,
                SQLChunk::Column(_) => 30,
                SQLChunk::Table(_) => 15,
                SQLChunk::Token(_) => 8,
                SQLChunk::Number(_) | SQLChunk::Param(_) => 4,
            });
            if matches!(chunk, SQLChunk::Param(_)) {
                param_cap = param_cap.saturating_add(1);
            }
        }

        (sql_cap.max(128), param_cap)
    }

    /// Returns an iterator over references to parameter values
    /// (avoids allocating a Vec - callers can collect if needed)
    #[inline]
    pub fn params(&self) -> impl Iterator<Item = &V> + use<'_, V> {
        self.chunks.iter().filter_map(|chunk| {
            if let SQLChunk::Param(Param {
                value: Some(value), ..
            }) = chunk
            {
                Some(value.as_ref())
            } else {
                None
            }
        })
    }

    /// Bind named parameters
    #[must_use]
    pub fn bind<T: SQLParam + Into<V>>(
        self,
        params: impl IntoIterator<Item: Into<ParamBind<'a, T>>>,
    ) -> Self {
        #[cfg(feature = "profiling")]
        profile_sql!("bind");

        let binds: SmallVec<[(&str, V); 4]> = params
            .into_iter()
            .map(Into::into)
            .map(|p| (p.name, p.value.into()))
            .collect();

        if binds.len() <= 4 {
            let bound_chunks: SmallVec<[SQLChunk<'a, V>; 8]> = self
                .chunks
                .into_iter()
                .map(|chunk| match chunk {
                    SQLChunk::Param(mut param) => {
                        if let Some(name) = param.placeholder.name
                            && let Some((_, value)) =
                                binds.iter().find(|(param_name, _)| *param_name == name)
                        {
                            param.value = Some(Cow::Owned(value.clone()));
                        }
                        SQLChunk::Param(param)
                    }
                    other => other,
                })
                .collect();

            return SQL {
                chunks: bound_chunks,
            };
        }

        let param_map: HashMap<&str, V> = binds.into_iter().collect();
        let bound_chunks: SmallVec<[SQLChunk<'a, V>; 8]> = self
            .chunks
            .into_iter()
            .map(|chunk| match chunk {
                SQLChunk::Param(mut param) => {
                    if let Some(name) = param.placeholder.name
                        && let Some(value) = param_map.get(name)
                    {
                        param.value = Some(Cow::Owned(value.clone()));
                    }
                    SQLChunk::Param(param)
                }
                other => other,
            })
            .collect();

        SQL {
            chunks: bound_chunks,
        }
    }
}

/// Tracks the `:name` parameters already bound for one `SQLite` statement.
///
/// `SQLite` gives every distinct parameter name a single slot, however often
/// the name appears, while each positional `?` takes its own slot. A value
/// list for the statement therefore holds one entry per distinct name, at the
/// position of the name's first occurrence.
#[derive(Default)]
pub(crate) struct SQLiteNamedParams<'n> {
    seen: SmallVec<[&'n str; 4]>,
}

impl<'n> SQLiteNamedParams<'n> {
    /// Records `name` and reports whether an earlier occurrence already took
    /// its slot.
    pub(crate) fn is_repeat(&mut self, name: &'n str) -> bool {
        if name.is_empty() {
            return false;
        }
        if self.seen.contains(&name) {
            true
        } else {
            self.seen.push(name);
            false
        }
    }
}

/// Canonical spacing logic for SQL chunk rendering.
/// Used by both `SQL::write_to()` and `prepare_render()`.
#[inline]
pub(crate) fn chunk_needs_space<V: SQLParam>(
    current: &SQLChunk<'_, V>,
    next: &SQLChunk<'_, V>,
) -> bool {
    // No space if current raw text ends with space
    if let SQLChunk::Raw(text) = current
        && text.ends_with(' ')
    {
        return false;
    }

    // No space if next raw text starts with space
    if let SQLChunk::Raw(text) = next
        && text.starts_with(' ')
    {
        return false;
    }

    match (current, next) {
        // No space before closing/separator punctuation
        // or after opening punctuation
        (_, SQLChunk::Token(Token::RPAREN | Token::COMMA | Token::SEMI | Token::DOT))
        | (SQLChunk::Token(Token::LPAREN | Token::DOT), _) => false,
        // Space after comma
        (SQLChunk::Token(Token::COMMA), _) => true,
        // Space after closing paren if next is word-like (e.g., ") FROM")
        (SQLChunk::Token(Token::RPAREN), next) => next.is_word_like(),
        // MySQL requires built-in function names to touch the opening
        // parenthesis unless the session enables IGNORE_SPACE. SQL::func uses
        // a raw static function name followed by LPAREN.
        (SQLChunk::Raw(_), SQLChunk::Token(Token::LPAREN))
            if V::DIALECT == crate::Dialect::MySQL =>
        {
            false
        }
        // Space before opening paren if preceded by word-like (e.g., "AS (")
        (current, SQLChunk::Token(Token::LPAREN)) => current.is_word_like(),
        // Space around comparison/arithmetic operators
        (SQLChunk::Token(t), _) if t.is_operator() => true,
        (_, SQLChunk::Token(t)) if t.is_operator() => true,
        // Space between all word-like chunks
        _ => current.is_word_like() && next.is_word_like(),
    }
}

// ==================== trait implementations ====================

impl<V: SQLParam> Default for SQL<'_, V> {
    #[inline]
    fn default() -> Self {
        Self::empty()
    }
}

impl<'a, V: SQLParam + 'a> From<&'a str> for SQL<'a, V> {
    #[inline]
    fn from(s: &'a str) -> Self {
        SQL::raw(s)
    }
}

impl<V: SQLParam> From<Token> for SQL<'_, V> {
    #[inline]
    fn from(value: Token) -> Self {
        SQL::token(value)
    }
}

impl<'a, V: SQLParam + 'a> AsRef<Self> for SQL<'a, V> {
    #[inline]
    fn as_ref(&self) -> &Self {
        self
    }
}

impl<V: SQLParam + core::fmt::Display> Display for SQL<'_, V> {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        // Collect params for Debug formatting (iterator can't be used with :?)
        let params: Vec<_> = self.params().collect();
        write!(f, r#"sql: "{}", params: {:?}"#, self.sql(), params)
    }
}

impl<'a, V: SQLParam + 'a> ToSQL<'a, V> for SQL<'a, V> {
    fn to_sql(&self) -> Self {
        self.clone()
    }

    fn into_sql(self) -> Self {
        self
    }
}

impl<'a, V: SQLParam, T> FromIterator<T> for SQL<'a, V>
where
    SQLChunk<'a, V>: From<T>,
{
    fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self {
        let chunks = iter
            .into_iter()
            .map(SQLChunk::from)
            .collect::<SmallVec<_>>();
        Self { chunks }
    }
}

impl<'a, V: SQLParam> IntoIterator for SQL<'a, V> {
    type Item = SQLChunk<'a, V>;
    type IntoIter = smallvec::IntoIter<[SQLChunk<'a, V>; 8]>;

    fn into_iter(self) -> Self::IntoIter {
        self.chunks.into_iter()
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::{Dialect, MySQLDialect};

    #[derive(Clone, Debug)]
    struct TestParam;

    impl SQLParam for TestParam {
        const DIALECT: Dialect = Dialect::MySQL;
        type DialectMarker = MySQLDialect;
    }

    impl From<TestParam> for Cow<'_, TestParam> {
        fn from(value: TestParam) -> Self {
            Cow::Owned(value)
        }
    }

    #[test]
    fn owning_mapped_params_preserves_every_chunk_kind() {
        let raw = String::from("COALESCE(");
        let identifier = String::from("display_name");
        let sql = SQL::raw(raw.as_str())
            .append(SQL::ident(identifier.as_str()))
            .push(Token::COMMA)
            .append(SQL::param(TestParam))
            .push(Token::COMMA)
            .push(Param::<TestParam>::from(Placeholder::named("fallback")))
            .push(Token::RPAREN);

        let owned = sql.into_owned_with(|value| value);
        drop(raw);
        drop(identifier);

        assert_eq!(owned.sql(), "COALESCE( `display_name`, ?, ?)");
        assert_eq!(owned.params().count(), 1);
        assert_eq!(
            owned
                .chunks
                .iter()
                .filter(|chunk| matches!(chunk, SQLChunk::Param(param) if param.value.is_none()))
                .count(),
            1
        );
    }

    #[test]
    fn columns_renders_an_identifier_list() {
        let columns = [
            ColumnRef::sql("users", "first"),
            ColumnRef::sql("users", "last`name"),
        ];

        assert_eq!(
            SQL::<TestParam>::columns(&columns).sql(),
            "`first`, `last``name`"
        );
    }

    #[test]
    fn select_star_uses_the_table_alias_to_qualify_columns() {
        let table = TableRef::sql("users", &["id", "name"]);
        let query = SQL::<TestParam>::from(Token::SELECT)
            .push(Token::FROM)
            .append(SQL::table(table).alias("u"));

        assert_eq!(
            query.sql(),
            "SELECT `u`.`id`, `u`.`name` FROM `users` AS `u`"
        );
    }

    #[test]
    fn nested_select_star_keeps_derived_alias_in_outer_projection() {
        let source = SQL::<TestParam>::from(Token::SELECT)
            .push(Token::FROM)
            .append(SQL::table(TableRef::sql("posts", &["id", "name"])))
            .parens()
            .push(Token::AS)
            .append(SQL::table(TableRef::sql("post_rows", &[])));
        let query = SQL::<TestParam>::from(Token::SELECT)
            .push(Token::FROM)
            .append(SQL::table(TableRef::sql("users", &["id"])))
            .append(SQL::raw(" INNER JOIN LATERAL "))
            .append(source)
            .push(Token::ON)
            .append(SQL::raw("TRUE"));

        assert_eq!(
            query.sql(),
            "SELECT `users`.`id`, `post_rows`.* FROM `users` INNER JOIN LATERAL (SELECT `posts`.`id`, `posts`.`name` FROM `posts`) AS `post_rows` ON TRUE"
        );
    }
}