Ted-Jiang commented on code in PR #3859:
URL: https://github.com/apache/arrow-datafusion/pull/3859#discussion_r997681735
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datafusion/optimizer/src/utils.rs:
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@@ -119,6 +119,121 @@ fn split_conjunction_owned_impl(expr: Expr, mut exprs:
Vec<Expr>) -> Vec<Expr> {
}
}
+/// Converts an expression to conjunctive normal form (CNF).
+///
+/// The following expression is in CNF:
+/// `(a OR b) AND (c OR d)`
+/// The following is not in CNF:
+/// `(a AND b) OR c`.
+/// But could be rewrite to a CNF expression:
+/// `(a OR c) AND (b OR c)`.
+///
+/// # Example
+/// ```
+/// # use datafusion_expr::{col, lit};
+/// # use datafusion_optimizer::utils::CnfHelper;
+/// // （a=1 AND b=2）OR c = 3
+/// let expr1 = col("a").eq(lit(1)).and(col("b").eq(lit(2)));
+/// let expr2 = col("c").eq(lit(3));
+/// let expr = expr1.or(expr2);
+///
+/// //（a=1 or c=3）AND（b=2 or c=3）
+/// let expr1 = col("a").eq(lit(1)).or(col("c").eq(lit(3)));
+/// let expr2 = col("b").eq(lit(2)).or(col("c").eq(lit(3)));
+/// let expect = expr1.and(expr2);
+/// // use split_conjunction_owned to split them
+/// assert_eq!(CnfHelper::new().rewrite_to_cnf_impl(&expr), expect);
+/// ```
+///
+pub struct CnfHelper {
+ max_count: usize,
+ current_count: usize,
+ exprs: Vec<Expr>,
+ original_expr: Option<Expr>,
+}
+
+impl CnfHelper {
+ pub fn new() -> Self {
+ CnfHelper {
+ max_count: 100,
+ current_count: 0,
+ exprs: vec![],
+ original_expr: None,
+ }
+ }
+
+ pub fn new_with_max_count(max_count: usize) -> Self {
+ CnfHelper {
+ max_count,
+ current_count: 0,
+ exprs: vec![],
+ original_expr: None,
+ }
+ }
+
+ fn increment_and_check_overload(&mut self) -> bool {
+ self.current_count += 1;
+ self.current_count >= self.max_count
+ }
+
+ pub fn rewrite_to_cnf_impl(&mut self, expr: &Expr) -> Expr {
Review Comment:
I will try this.
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