feat: add SelectExprTrait for ergonomic alias and window chaining

[yuly3]

PR Info

• Closes Improve DX for alias and window #344

Changes

SelectExprTrait

Add SelectExprTrait providing alias and over methods. Implemented for both SelectExpr and T: Into<Expr>, enabling.

Expr::col(...).alias(...)
Expr::col(...).over(...)

over accepts impl Into<WindowSelectType>, with impls for

impl From<WindowStatement> for WindowSelectType;
impl<T: IntoIden> From<T> for WindowSelectType;

Compatibility and refactor

Existing helpers are kept, and their implementation now routes through SelectExprTrait.

• SelectStatement::expr_as
• SelectStatement::expr_window
• SelectStatement::expr_window_as
• SelectStatement::expr_window_name
• SelectStatement::expr_window_name_as

Doctest fixes

Fix window-related doctests to generate executable SQL (apply the window clause to a window function, e.g. MAX(col) OVER (...), instead of a bare column).

Examples

Query::select()
    .from(Char::Table)
    .expr(Expr::col(Char::Character).alias("C"));

Query::select()
    .from(Char::Table)
    .expr(
        Expr::col(Char::Character)
            .max()
            .over(WindowStatement::partition_by(Char::FontSize))
            .alias("C"),
    );

Query::select()
    .from(Char::Table)
    .expr(Expr::col(Char::Character).max().over("w"))
    .window("w", WindowStatement::partition_by(Char::FontSize));

Design notes & feedback requested

I'd appreciate maintainer input on whether this design aligns with the project's long-term direction.

1. Expr → SelectExpr transition

   • Option A: Explicit method like Expr::into_select() — more explicit, avoids method-name collisions
   • Option B: Extension trait allowing Expr::col(...).alias(...) directly — more ergonomic (this PR)

2. SelectExpr construction responsibility

   • Option A: Chaining methods on SelectExpr (this PR) — simple, but moves SelectExpr toward a builder-like role
   • Option B: Separate SelectExprBuilder — keeps SelectExpr as pure data, but adds a new public type

[Huliiiiii]

Add impls for WindowSelectType

impl From<WindowStatement> for WindowSelectType;
impl<T: IntoIden> From<T> for WindowSelectType;

Replace window and window_name with over

fn over(mut self, over_expr: impl Into<WindowSelectType>) -> SelectExpr;

[yuly3]

Thanks for the feedback!
I've implemented the changes you suggested.

[github-actions]

🎉 Released In 1.0.0-rc.33 🎉

Thank you everyone for the contribution!
This feature is now available in the latest release. Now is a good time to upgrade!
Your participation is what makes us unique; your adoption is what drives us forward.
You can support SeaQL 🌊 by starring our repos, sharing our libraries and becoming a sponsor ⭐.