Add a few more comments

datafusion/sqllogictest/test_files/expr.slt

@@ -1660,6 +1660,9 @@ SELECT regexp_match('aaa-0', NULL);
 ----
 NULL
 
+##### csv_query_nullif_divide_by_0
+
+
 statement ok
 CREATE EXTERNAL TABLE aggregate_test_100_by_sql (
   c1  VARCHAR NOT NULL,
@@ -1680,6 +1683,8 @@ STORED AS CSV
 WITH HEADER ROW
 LOCATION '../../testing/data/csv/aggregate_test_100.csv'
 
+
+
 query I
 SELECT c8/nullif(c7, 0) FROM aggregate_test_100_by_sql LIMIT 9 OFFSET 81;
 ----
@@ -1693,7 +1698,7 @@ NULL
 671
 203
 
-# nested_subquery()
+#### nested_subquery()
 statement ok
 CREATE TABLE test_t1 (
     id INT,
@@ -1706,14 +1711,14 @@ CREATE TABLE test_t2 (
     a INT
 )
 
-#  the purpose of this test is just to make sure the query produces a valid plan
+# the purpose of this test is just to make sure the query produces a valid plan
 query I
 SELECT COUNT(*) as cnt FROM ((SELECT id FROM test_t1) EXCEPT (SELECT id FROM test_t2)) foo;
 ----
 0
 
 
-# comparisons_with_null_lt
+#### comparisons_with_null_lt
 
 # 1. Numeric comparison with NULL
 query B
@@ -1766,6 +1771,12 @@ select column2 < NULL from (VALUES (1, 'foo' ,2.3), (2, 'bar', 5.4)) as t;
 NULL
 NULL
 
+#####
+# same queries, reversed argument order (as they go through
+# a different evaluation path)
+#####
+
+# Boolean comparison with NULL
 query B
 select column1 < NULL from (VALUES (true), (false)) as t;
 ----
@@ -1808,24 +1819,30 @@ select NULL != column1 from (VALUES (1, 'foo' ,2.3), (2, 'bar', 5.4)) as t;
 NULL
 NULL
 
+# 1.1 Float value comparison with NULL
 query B
 select NULL < column3 from (VALUES (1, 'foo' ,2.3), (2, 'bar', 5.4)) as t;
 ----
 NULL
 NULL
 
+# String comparison with NULL
 query B
 select NULL < column2 from (VALUES (1, 'foo' ,2.3), (2, 'bar', 5.4)) as t;
 ----
 NULL
 NULL
 
+# Boolean comparison with NULL
 query B
 select NULL < column1 from (VALUES (true), (false)) as t;
 ----
 NULL
 NULL
 
+#### binary_mathematical_operator_with_null_lt
+
+# 1. Integer and NULL
 query I
 select column1 + NULL from (VALUES (1, 2.3), (2, 5.4)) as t;
 ----
@@ -1850,6 +1867,7 @@ select column1 % NULL from (VALUES (1, 2.3), (2, 5.4)) as t;
 NULL
 NULL
 
+# 2. Float and NULL
 query R
 select column2 + NULL from (VALUES (1, 2.3), (2, 5.4)) as t;
 ----
@@ -1880,6 +1898,12 @@ select column2 % NULL from (VALUES (1, 2.3), (2, 5.4)) as t;
 NULL
 NULL
 
+#####
+# same queries, reversed argument order (as they go through
+# a different evaluation path)
+#####
+
+# 3. NULL and Integer
 query I
 select NULL + column1 from (VALUES (1, 2.3), (2, 5.4)) as t;
 ----
@@ -1910,6 +1934,8 @@ select NULL % column1 from (VALUES (1, 2.3), (2, 5.4)) as t;
 NULL
 NULL
 
+# 4. NULL and Float
+
 query R
 select NULL + column2 from (VALUES (1, 2.3), (2, 5.4)) as t;
 ----
@@ -1941,6 +1967,8 @@ NULL
 NULL
 
 
+# query_binary_eq
+
 statement ok
 CREATE TABLE t_source(
     column1 String,