Modify the code as suggested and fix merge conflict

src/ast/operator.rs

@@ -51,6 +51,8 @@ pub enum UnaryOperator {
     PGPrefixFactorial,
     /// Absolute value, e.g. `@ -9` (PostgreSQL-specific)
     PGAbs,
+    /// Unary logical not operator: e.g. `! false` (Hive-specific)
+    BangNot,
 }
 
 impl fmt::Display for UnaryOperator {
@@ -65,6 +67,7 @@ impl fmt::Display for UnaryOperator {
             UnaryOperator::PGPostfixFactorial => "!",
             UnaryOperator::PGPrefixFactorial => "!!",
             UnaryOperator::PGAbs => "@",
+            UnaryOperator::BangNot => "!",
         })
     }
 }

src/dialect/hive.rs

@@ -51,4 +51,8 @@ impl Dialect for HiveDialect {
     fn require_interval_qualifier(&self) -> bool {
         true
     }
+
+    fn supports_bang_not_operator(&self) -> bool {
+        true
+    }
 }

src/dialect/mod.rs

@@ -575,6 +575,11 @@ pub trait Dialect: Debug + Any {
         false
     }
 
+    /// Returns true if the dialect supports `a!` expressions
+    fn supports_factorial_operator(&self) -> bool {
+        false
+    }
+
     /// Returns true if this dialect supports treating the equals operator `=` within a `SelectItem`
     /// as an alias assignment operator, rather than a boolean expression.
     /// For example: the following statements are equivalent for such a dialect:
@@ -590,6 +595,11 @@ pub trait Dialect: Debug + Any {
     fn supports_try_convert(&self) -> bool {
         false
     }
+
+    /// Returns true if the dialect supports `!a` expressions
+    fn supports_bang_not_operator(&self) -> bool {
+        false
+    }
 }
 
 /// This represents the operators for which precedence must be defined

src/dialect/postgresql.rs

@@ -191,6 +191,11 @@ impl Dialect for PostgreSqlDialect {
     fn supports_explain_with_utility_options(&self) -> bool {
         true
     }
+
+    /// see <https://www.postgresql.org/docs/13/functions-math.html>
+    fn supports_factorial_operator(&self) -> bool {
+        true
+    }
 }
 
 pub fn parse_comment(parser: &mut Parser) -> Result<Statement, ParserError> {

src/parser/mod.rs

@@ -1175,6 +1175,14 @@ impl<'a> Parser<'a> {
                     ),
                 })
             }
+            Token::ExclamationMark if self.dialect.supports_bang_not_operator() => {
+                Ok(Expr::UnaryOp {
+                    op: UnaryOperator::BangNot,
+                    expr: Box::new(
+                        self.parse_subexpr(self.dialect.prec_value(Precedence::UnaryNot))?,
+                    ),
+                })
+            }
             tok @ Token::DoubleExclamationMark
             | tok @ Token::PGSquareRoot
             | tok @ Token::PGCubeRoot
@@ -1268,7 +1276,6 @@ impl<'a> Parser<'a> {
             }
             _ => self.expected("an expression", next_token),
         }?;
-
         if self.parse_keyword(Keyword::COLLATE) {
             Ok(Expr::Collate {
                 expr: Box::new(expr),
@@ -2028,6 +2035,13 @@ impl<'a> Parser<'a> {
         }
     }
 
+    pub fn parse_bang_not(&mut self) -> Result<Expr, ParserError> {
+        Ok(Expr::UnaryOp {
+            op: UnaryOperator::BangNot,
+            expr: Box::new(self.parse_subexpr(self.dialect.prec_value(Precedence::UnaryNot))?),
+        })
+    }
+
     /// Parses fulltext expressions [`sqlparser::ast::Expr::MatchAgainst`]
     ///
     /// # Errors
@@ -2800,11 +2814,40 @@ impl<'a> Parser<'a> {
                 format: None,
             })
         } else if Token::ExclamationMark == tok {
-            // PostgreSQL factorial operation
-            Ok(Expr::UnaryOp {
-                op: UnaryOperator::PGPostfixFactorial,
-                expr: Box::new(expr),
-            })
+            if self.dialect.supports_factorial_operator() {
+                match expr {
+                    Expr::Value(_) | Expr::Identifier(_) | Expr::Nested(_) | Expr::BinaryOp{..} => Ok(Expr::UnaryOp {
+                        op: UnaryOperator::PGPostfixFactorial,
+                        expr: Box::new(expr),
+                    }),
+                    _ => {
+                        self.expected(
+                            "Value or Identifier or  Nested or BinaryOp struct before factorial operator(!)", self.peek_token())
+                    },
+                }
+            } else if self.dialect.supports_bang_not_operator() {
+                let token = self.next_token();
+                match token.token {
+                    Token::Word(_) | Token::Number(..) => Ok(Expr::UnaryOp {
+                        op: UnaryOperator::BangNot,
+                        expr: Box::new(expr),
+                    }),
+                    _ => {
+                        parser_err!(
+                            "current dialect support bang not operator, but with wrong synx",
+                            tok.location
+                        )
+                    }
+                }
+            } else {
+                parser_err!(
+                    format!(
+                        "current dialect: {:?} does not support factorial operator or bang not operator",
+                        self.dialect
+                    ),
+                    self.peek_token().location
+                )
+            }
         } else if Token::LBracket == tok {
             if dialect_of!(self is PostgreSqlDialect | DuckDbDialect | GenericDialect) {
                 self.parse_subscript(expr)

tests/sqlparser_common.rs

@@ -11460,3 +11460,49 @@ fn test_try_convert() {
         all_dialects_where(|d| d.supports_try_convert() && !d.convert_type_before_value());
     dialects.verified_expr("TRY_CONVERT('foo', VARCHAR(MAX))");
 }
+
+#[test]
+fn parse_bang_not() {
+    let dialects = all_dialects_where(|d| d.supports_bang_not_operator());
+    let sql = "SELECT !a, !(b > 3)";
+    let Select { projection, .. } = dialects.verified_only_select(sql);
+
+    for (i, (op, expr)) in [
+        (
+            UnaryOperator::BangNot,
+            Box::new(Expr::Identifier(Ident::new("a"))),
+        ),
+        (
+            UnaryOperator::BangNot,
+            Box::new(Expr::Nested(Box::new(Expr::BinaryOp {
+                left: Box::new(Expr::Identifier(Ident::new("b"))),
+                op: BinaryOperator::Gt,
+                right: Box::new(Expr::Value(Value::Number("3".parse().unwrap(), false))),
+            }))),
+        ),
+    ]
+    .into_iter()
+    .enumerate()
+    {
+        assert_eq!(
+            SelectItem::UnnamedExpr(Expr::UnaryOp { op: op, expr }),
+            projection[i]
+        )
+    }
+
+    let sql = "SELECT a!";
+    assert_eq!(
+        dialects.parse_sql_statements(sql).unwrap_err(),
+        ParserError::ParserError(
+            "current dialect support bang not operator, but with wrong synx".to_string()
+        )
+    );
+
+    let sql = "SELECT !a";
+    assert_eq!(
+        all_dialects_where(|d| !d.supports_bang_not_operator())
+            .parse_sql_statements(sql)
+            .unwrap_err(),
+        ParserError::ParserError("Expected: an expression, found: !".to_string())
+    );
+}