From 83104b7b697b6bc2d4787a0cb0ea4708dbe9c7a6 Mon Sep 17 00:00:00 2001
From: Nyall Dawson <nyall.dawson@gmail.com>
Date: Sun, 23 Aug 2020 07:55:41 +1000
Subject: [PATCH] Setup operator precedence for parser to avoid ambiguity and
 fix shift/reduce warnings

---
 src/sql/lexer.l  | 11 +++++++----
 src/sql/parser.y | 18 +++++++++++++++---
 2 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/src/sql/lexer.l b/src/sql/lexer.l
index 7a2123c..5bea481 100644
--- a/src/sql/lexer.l
+++ b/src/sql/lexer.l
@@ -50,25 +50,28 @@ struct sql_context;
 
 
 %%
-select	{ return SELECT; }
+select		{ return SELECT; }
 from		{ return FROM; }
 connect	{ return CONNECT; }
 disconnect	{ return DISCONNECT; }
 to		{ return TO; }
 list		{ return LIST; }
 where		{ return WHERE; }
-tables	{ return TABLES; }
-table	{ return TABLE; }
+tables		{ return TABLES; }
+table		{ return TABLE; }
 describe	{ return DESCRIBE; }
 and		{ return AND; }
 or		{ return OR; }
 not		{ return NOT; }
 is		{ return IS; }
 null		{ return NUL; }
+"="		{ return EQ; }
 (<=)		{ return LTEQ; }
 (>=)		{ return GTEQ; }
+"<"		{ return LT; }
+">"		{ return GT; }
 like		{ return LIKE; }
-limit	{ return LIMIT; }
+limit		{ return LIMIT; }
 count		{ return COUNT; }
 strptime	{ return STRPTIME; }
 [ \t\r]	;
diff --git a/src/sql/parser.y b/src/sql/parser.y
index 2effb96..0524bf1 100644
--- a/src/sql/parser.y
+++ b/src/sql/parser.y
@@ -71,6 +71,18 @@ typedef struct sql_context
 %type <ival> nulloperator
 %type <name> identifier
 
+//
+// operator precedence
+//
+
+// left associativity means that 1+2+3 translates to (1+2)+3
+// the order of operators here determines their precedence
+
+%left OR
+%left AND
+%right NOT
+%left EQ LTEQ GTEQ LT GT LIKE IS
+
 %%
 
 stmt:
@@ -142,9 +154,9 @@ identifier:
 	;
 
 operator:
-	'='	{ $$ = MDB_EQUAL; }
-	| '>'	{ $$ = MDB_GT; }
-	| '<'	{ $$ = MDB_LT; }
+	EQ	{ $$ = MDB_EQUAL; }
+	| GT	{ $$ = MDB_GT; }
+	| LT	{ $$ = MDB_LT; }
 	| LTEQ	{ $$ = MDB_LTEQ; }
 	| GTEQ	{ $$ = MDB_GTEQ; }
 	| LIKE	{ $$ = MDB_LIKE; }