Bug#23411: ... MOD-ing zero returns strange result

  
The Item_func_mod objects never had maybe_null set, so users had no reason 
to expect that they can be NULL, and may therefore deduce wrong results.
Now, set maybe_null.


mysql-test/r/func_test.result:
  Verify that the predictions are true.
mysql-test/t/func_test.test:
  Verify that the predictions are true.
sql/item_func.cc:
  MOD functions may be NULL.

1 files changed, 32 insertions, 0 deletions

diff --git a/mysql-test/t/func_test.test b/mysql-test/t/func_test.test
index 2ad64b6c5a6..99519b54ca6 100644
--- a/mysql-test/t/func_test.test
+++ b/mysql-test/t/func_test.test
@@ -108,4 +108,36 @@ select 5.1 mod 3, 5.1 mod -3, -5.1 mod 3, -5.1 mod -3;
 
 select 5 mod 3, 5 mod -3, -5 mod 3, -5 mod -3;
 
+#
+# Bug#23411: The "%" (MOD) operator is not documented; MOD-ing zero returns strange result
+# Manual: "Division by zero produces a NULL result"
+#
+select (12%0) <=> null      as '1';
+select (12%0) is null       as '1';
+select 12%0                 as 'NULL';
+select 12%2                 as '0';
+select 12%NULL              as 'NULL';
+select 12 % null            as 'NULL';
+select null % 12            as 'NULL';
+select null % 0             as 'NULL';
+select 0 % null             as 'NULL';
+select null % null          as 'NULL';
+
+select (12 mod 0) <=> null  as '1';
+select (12 mod 0) is null   as '1';
+select 12 mod 0             as 'NULL';
+select 12 mod 2             as '0';
+select 12 mod null          as 'NULL';
+select null mod 12          as 'NULL';
+select null mod 0           as 'NULL';
+select 0 mod null           as 'NULL';
+select null mod null        as 'NULL';
+
+select mod(12.0, 0)         as 'NULL';
+select mod(12, 0.0)         as 'NULL';
+select mod(12, NULL)        as 'NULL';
+select mod(12.0, NULL)      as 'NULL';
+select mod(NULL, 2)         as 'NULL';
+select mod(NULL, 2.0)       as 'NULL';
+
 # End of 4.1 tests