fix: Correct INTERVAL + INTERVAL expression parsing

Author: MazterQyou

src/parser.rs

@@ -1026,7 +1026,7 @@ impl<'a> Parser<'a> {
 
         // The first token in an interval is a string literal which specifies
         // the duration of the interval.
-        let value = self.parse_expr()?;
+        let value = self.parse_subexpr(Self::PLUS_MINUS_PREC)?;
 
         // Following the string literal is a qualifier which indicates the units
         // of the duration specified in the string literal.

tests/sqlparser_common.rs

@@ -2708,6 +2708,59 @@ fn parse_literal_interval() {
     );
 }
 
+#[test]
+fn parse_interval_math() {
+    let sql = "SELECT INTERVAL '1 DAY' + INTERVAL '2 DAY'";
+    let select = verified_only_select(sql);
+    assert_eq!(
+        &Expr::BinaryOp {
+            left: Box::new(Expr::Value(Value::Interval {
+                value: Box::new(Expr::Value(Value::SingleQuotedString("1 DAY".to_string()))),
+                leading_field: None,
+                leading_precision: None,
+                last_field: None,
+                fractional_seconds_precision: None,
+            })),
+            op: BinaryOperator::Plus,
+            right: Box::new(Expr::Value(Value::Interval {
+                value: Box::new(Expr::Value(Value::SingleQuotedString("2 DAY".to_string()))),
+                leading_field: None,
+                leading_precision: None,
+                last_field: None,
+                fractional_seconds_precision: None,
+            })),
+        },
+        expr_from_projection(only(&select.projection)),
+    );
+
+    let sql = "SELECT INTERVAL '1' || ' DAY' + INTERVAL '2 DAY'";
+    let select = verified_only_select(sql);
+    assert_eq!(
+        &Expr::BinaryOp {
+            left: Box::new(Expr::Value(Value::Interval {
+                value: Box::new(Expr::BinaryOp {
+                    left: Box::new(Expr::Value(Value::SingleQuotedString("1".to_string()))),
+                    op: BinaryOperator::StringConcat,
+                    right: Box::new(Expr::Value(Value::SingleQuotedString(" DAY".to_string()))),
+                }),
+                leading_field: None,
+                leading_precision: None,
+                last_field: None,
+                fractional_seconds_precision: None,
+            })),
+            op: BinaryOperator::Plus,
+            right: Box::new(Expr::Value(Value::Interval {
+                value: Box::new(Expr::Value(Value::SingleQuotedString("2 DAY".to_string()))),
+                leading_field: None,
+                leading_precision: None,
+                last_field: None,
+                fractional_seconds_precision: None,
+            })),
+        },
+        expr_from_projection(only(&select.projection)),
+    );
+}
+
 #[test]
 fn parse_at_timezone() {
     let zero = Expr::Value(number("0"));