Lordworms commented on issue #9495:
URL:
https://github.com/apache/arrow-datafusion/issues/9495#issuecomment-1984954313
Since We have so many Expr
```Rust
pub enum Expr {
/// An expression with a specific name.
Alias(Alias),
/// A named reference to a qualified filed in a schema.
Column(Column),
/// A named reference to a variable in a registry.
ScalarVariable(DataType, Vec<String>),
/// A constant value.
Literal(ScalarValue),
/// A binary expression such as "age > 21"
BinaryExpr(BinaryExpr),
/// LIKE expression
Like(Like),
/// LIKE expression that uses regular expressions
SimilarTo(Like),
/// Negation of an expression. The expression's type must be a boolean
to make sense.
Not(Box<Expr>),
/// True if argument is not NULL, false otherwise. This expression
itself is never NULL.
IsNotNull(Box<Expr>),
/// True if argument is NULL, false otherwise. This expression itself is
never NULL.
IsNull(Box<Expr>),
/// True if argument is true, false otherwise. This expression itself is
never NULL.
IsTrue(Box<Expr>),
/// True if argument is false, false otherwise. This expression itself
is never NULL.
IsFalse(Box<Expr>),
/// True if argument is NULL, false otherwise. This expression itself is
never NULL.
IsUnknown(Box<Expr>),
/// True if argument is FALSE or NULL, false otherwise. This expression
itself is never NULL.
IsNotTrue(Box<Expr>),
/// True if argument is TRUE OR NULL, false otherwise. This expression
itself is never NULL.
IsNotFalse(Box<Expr>),
/// True if argument is TRUE or FALSE, false otherwise. This expression
itself is never NULL.
IsNotUnknown(Box<Expr>),
/// arithmetic negation of an expression, the operand must be of a
signed numeric data type
Negative(Box<Expr>),
/// Returns the field of a [`arrow::array::ListArray`] or
/// [`arrow::array::StructArray`] by index or range
GetIndexedField(GetIndexedField),
/// Whether an expression is between a given range.
Between(Between),
/// The CASE expression is similar to a series of nested if/else and
there are two forms that
/// can be used. The first form consists of a series of boolean "when"
expressions with
/// corresponding "then" expressions, and an optional "else" expression.
///
/// CASE WHEN condition THEN result
/// [WHEN ...]
/// [ELSE result]
/// END
///
/// The second form uses a base expression and then a series of "when"
clauses that match on a
/// literal value.
///
/// CASE expression
/// WHEN value THEN result
/// [WHEN ...]
/// [ELSE result]
/// END
Case(Case),
/// Casts the expression to a given type and will return a runtime error
if the expression cannot be cast.
/// This expression is guaranteed to have a fixed type.
Cast(Cast),
/// Casts the expression to a given type and will return a null value if
the expression cannot be cast.
/// This expression is guaranteed to have a fixed type.
TryCast(TryCast),
/// A sort expression, that can be used to sort values.
Sort(Sort),
/// Represents the call of a scalar function with a set of arguments.
ScalarFunction(ScalarFunction),
/// Represents the call of an aggregate built-in function with arguments.
AggregateFunction(AggregateFunction),
/// Represents the call of a window function with arguments.
WindowFunction(WindowFunction),
/// Returns whether the list contains the expr value.
InList(InList),
/// EXISTS subquery
Exists(Exists),
/// IN subquery
InSubquery(InSubquery),
/// Scalar subquery
ScalarSubquery(Subquery),
/// Represents a reference to all available fields in a specific schema,
/// with an optional (schema) qualifier.
///
/// This expr has to be resolved to a list of columns before translating
logical
/// plan into physical plan.
Wildcard { qualifier: Option<String> },
/// List of grouping set expressions. Only valid in the context of an
aggregate
/// GROUP BY expression list
GroupingSet(GroupingSet),
/// A place holder for parameters in a prepared statement
/// (e.g. `$foo` or `$1`)
Placeholder(Placeholder),
/// A place holder which hold a reference to a qualified field
/// in the outer query, used for correlated sub queries.
OuterReferenceColumn(DataType, Column),
/// Unnest expression
Unnest(Unnest),
}
```
Guess we can use a Trait to split the workload. I'd like to pick up some of
them
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