Setup operator precedence for parser to avoid ambiguity and fix shift/reduce warnings

src/sql/lexer.l

@@ -65,8 +65,11 @@ 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; }
 count		{ return COUNT; }

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:
-	'='	{ $$ = MDB_EQUAL; }
+	EQ	{ $$ = MDB_EQUAL; }
-	| '>'	{ $$ = MDB_GT; }
+	| GT	{ $$ = MDB_GT; }
-	| '<'	{ $$ = MDB_LT; }
+	| LT	{ $$ = MDB_LT; }
 	| LTEQ	{ $$ = MDB_LTEQ; }
 	| GTEQ	{ $$ = MDB_GTEQ; }
 	| LIKE	{ $$ = MDB_LIKE; }