Add a test showing how negative constants are parsed (#1421)

tests/sqlparser_common.rs

@@ -42,7 +42,7 @@ mod test_utils;
 
 #[cfg(test)]
 use pretty_assertions::assert_eq;
-use sqlparser::ast::Expr::Identifier;
+use sqlparser::ast::Expr::{Identifier, UnaryOp};
 use sqlparser::test_utils::all_dialects_except;
 
 #[test]
@@ -4778,6 +4778,33 @@ fn parse_aggregate_with_group_by() {
     //TODO: assertions
 }
 
+#[test]
+fn parse_literal_integer() {
+    let sql = "SELECT 1, -10, +20";
+    let select = verified_only_select(sql);
+    assert_eq!(3, select.projection.len());
+    assert_eq!(
+        &Expr::Value(number("1")),
+        expr_from_projection(&select.projection[0]),
+    );
+    // negative literal is parsed as a - and expr
+    assert_eq!(
+        &UnaryOp {
+            op: UnaryOperator::Minus,
+            expr: Box::new(Expr::Value(number("10")))
+        },
+        expr_from_projection(&select.projection[1]),
+    );
+    // positive literal is parsed as a + and expr
+    assert_eq!(
+        &UnaryOp {
+            op: UnaryOperator::Plus,
+            expr: Box::new(Expr::Value(number("20")))
+        },
+        expr_from_projection(&select.projection[2]),
+    )
+}
+
 #[test]
 fn parse_literal_decimal() {
     // These numbers were explicitly chosen to not roundtrip if represented as