feat(expr): implement greatest and least function (#12838)

e2e_test/batch/functions/greatest_least.slt.part

@@ -0,0 +1,73 @@
+statement ok
+create table t(id int, v1 int2, v2 int4, v3 int8);
+
+statement ok
+insert into t values (1, 1, 2, 3), (2, 2, NULL, 5), (3, NULL, NULL, 8), (4, NULL, NULL, NULL);
+
+statement ok
+flush;
+
+statement error
+select greatest(v1, '123');
+
+statement error
+select greatest();
+
+statement error
+select least();
+
+query I
+select greatest(1, 2, 3);
+----
+3
+
+query I
+select greatest(2);
+----
+2
+
+query I
+select least(1, 2, 3);
+----
+1
+
+query I
+select least(2);
+----
+2
+
+query I
+select greatest(v1, v2, v3) from t order by id;
+----
+3
+5
+8
+NULL
+
+query I
+select least(v1, v2, v3) from t order by id;
+----
+1
+2
+8
+NULL
+
+query I
+select greatest(7, v3) from t order by id;
+----
+7
+7
+8
+7
+
+query I
+select least(NULL, v1, 2) from t order by id;
+----
+1
+2
+2
+2
+
+
+statement ok
+drop table t;

proto/expr.proto

@@ -33,6 +33,8 @@ message ExprNode {
     LESS_THAN_OR_EQUAL = 11;
     GREATER_THAN = 12;
     GREATER_THAN_OR_EQUAL = 13;
+    GREATEST = 14;
+    LEAST = 15;
     // logical operators
     AND = 21;
     OR = 22;