Implement prettier SQL unparsing (more human readable)

datafusion/expr/src/operator.rs

@@ -218,37 +218,33 @@ impl Operator {
     }
 
     /// Get the operator precedence
-    /// use <https://www.postgresql.org/docs/7.0/operators.htm#AEN2026> as a reference
+    /// use <https://www.postgresql.org/docs/7.2/sql-precedence.html> as a reference
     pub fn precedence(&self) -> u8 {
         match self {
             Operator::Or => 5,
             Operator::And => 10,
-            Operator::NotEq
-            | Operator::Eq
-            | Operator::Lt
-            | Operator::LtEq
-            | Operator::Gt
-            | Operator::GtEq => 20,
-            Operator::Plus | Operator::Minus => 30,
-            Operator::Multiply | Operator::Divide | Operator::Modulo => 40,
+            Operator::Eq | Operator::NotEq | Operator::LtEq | Operator::GtEq => 15,
+            Operator::Lt | Operator::Gt => 20,
+            Operator::LikeMatch
+            | Operator::NotLikeMatch
+            | Operator::ILikeMatch
+            | Operator::NotILikeMatch => 25,
             Operator::IsDistinctFrom
             | Operator::IsNotDistinctFrom
             | Operator::RegexMatch
             | Operator::RegexNotMatch
             | Operator::RegexIMatch
             | Operator::RegexNotIMatch
-            | Operator::LikeMatch
-            | Operator::ILikeMatch
-            | Operator::NotLikeMatch
-            | Operator::NotILikeMatch
             | Operator::BitwiseAnd
             | Operator::BitwiseOr
             | Operator::BitwiseShiftLeft
             | Operator::BitwiseShiftRight
             | Operator::BitwiseXor
             | Operator::StringConcat
             | Operator::AtArrow
-            | Operator::ArrowAt => 0,
+            | Operator::ArrowAt => 30,
+            Operator::Plus | Operator::Minus => 40,
+            Operator::Multiply | Operator::Divide | Operator::Modulo => 45,
         }
     }
 }