[IMPALA-4877] Incorrect precedence of unary minus and plus

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: Impala 2.8.0
• Fix Version/s: Impala 2.9.0
• Component/s: Frontend
• Target Version: Impala 2.9.0
• Assignee: Daniel Hecht
• Reporter: Daniel Hecht
• Created: 03/Feb/17 17:53
• Updated: 01/Mar/17 17:46
• Resolved: 01/Mar/17 17:46

Description

Impala's parser gives unary - and unary + the same precedence as binary + and -, which has lower precedence than other binary operators, such as / and *. This leads to strange typing, especially apparent due to the heuristics of Expr.convertNumericLiteralsFromDecimal() (see also IMPALA-3437).

For example, division between positive decimal numbers performs decimal divide, as expected:

> select typeof(1.0 / 3.0);
+-------------------+
| typeof(1.0 / 3.0) |
+-------------------+
| DECIMAL(6,4)      |
+-------------------+
> select 1.0 / 3.0;
+-----------+
| 1.0 / 3.0 |
+-----------+
| 0.3333    |
+-----------+

But if you add unary minus, things get weird:

> select typeof(-1.0 / 3.0);
+------------------------+
| typeof(-1 * 1.0 / 3.0) |
+------------------------+
| DOUBLE                 |
+------------------------+
> select -1.0 / 3.0;
+---------------------+
| -1 * 1.0 / 3.0      |
+---------------------+
| -0.3333333333333333 |
+---------------------+

Other examples involving integers:

> select -1 & 3;
+------------+
| -1 * 1 & 3 |
+------------+
| -1         |
+------------+

A workaround is to use parenthesis to force the correct parsing:

> select (-1.0) / 3.0;
+--------------+
| (-1.0) / 3.0 |
+--------------+
| -0.3333      |
+--------------+
> select (-1) & 3;
+----------+
| (-1) & 3 |
+----------+
| 3        |
+----------+

The fix is to define higher precedence levels for unary minus/plus. Something like:

diff --git a/fe/src/main/cup/sql-parser.cup b/fe/src/main/cup/sql-parser.cup
index 33f0591..d3af3be 100644
--- a/fe/src/main/cup/sql-parser.cup
+++ b/fe/src/main/cup/sql-parser.cup
@@ -272,7 +272,7 @@ terminal
   KW_WHERE, KW_WITH;

 terminal COLON, SEMICOLON, COMMA, DOT, DOTDOTDOT, STAR, LPAREN, RPAREN, LBRACKET,
-  RBRACKET, DIVIDE, MOD, ADD, SUBTRACT;
+  RBRACKET, DIVIDE, MOD, ADD, SUBTRACT, UMINUS, UADD;
 terminal BITAND, BITOR, BITXOR, BITNOT;
 terminal EQUAL, NOT, NOTEQUAL, LESSTHAN, GREATERTHAN;
 terminal FACTORIAL; // Placeholder terminal for postfix factorial operator
@@ -511,6 +511,7 @@ precedence left EQUAL, NOTEQUAL, LESSTHAN, GREATERTHAN, KW_FROM, KW_DISTINCT;
 precedence left ADD, SUBTRACT;
 precedence left STAR, DIVIDE, MOD, KW_DIV;
 precedence left BITAND, BITOR, BITXOR, BITNOT;
+precedence left UMINUS, UADD;
 precedence left FACTORIAL;
 precedence left KW_ORDER, KW_BY, KW_LIMIT;
 precedence left LPAREN, RPAREN;
@@ -2591,8 +2592,10 @@ sign_chain_expr ::=
                                   new NumericLiteral(BigDecimal.valueOf(-1)), e);
     }
   :}
+  %prec UMINUS
   | ADD expr:e
   {: RESULT = e; :}
+  %prec UADD
   ;

 expr ::=