Bug#35323398: Assertion 'scale >= 0 && precision > 0 and

              scale <= precision' failed

The problem is with the resolve_type_inner() function for class
Item_func_nullif. If the original data type is a temporal type,
the type is adjusted to a string type. However, the result type
is not adjusted accordingly, which may cause later inconsistencies.

Fixed by setting result type to STRING_RESULT.

Change-Id: I91b43741ced9c0253b9e337e7170d8c93ac9c8f4

Author: roylyseng

mysql-test/r/func_if.result

@@ -343,3 +343,14 @@ Warning	1292	Incorrect datetime value: '13339'
 DO CAST(UNIX_TIMESTAMP(CASE 1 WHEN 1 THEN 42 ELSE 42 END) AS UNSIGNED);
 Warnings:
 Warning	1292	Incorrect datetime value: '42'
+# Bug#35323398: Assertion 'scale >= 0 && precision > 0 and
+#               scale <= precision' failed
+SELECT AVG(NULLIF(YEAR('2001-01-01'),10));
+AVG(NULLIF(YEAR('2001-01-01'),10))
+2001
+CREATE TABLE t1(y YEAR);
+INSERT INTO t1 VALUES(2001);
+SELECT AVG(NULLIF(y, 10)) FROM t1;
+AVG(NULLIF(y, 10))
+2001
+DROP TABLE t1;

mysql-test/t/func_if.test

@@ -299,3 +299,15 @@ DROP TABLE t;
 
 DO CAST(UNIX_TIMESTAMP(IF('',3,13339)) AS UNSIGNED);
 DO CAST(UNIX_TIMESTAMP(CASE 1 WHEN 1 THEN 42 ELSE 42 END) AS UNSIGNED);
+
+--echo # Bug#35323398: Assertion 'scale >= 0 && precision > 0 and
+--echo #               scale <= precision' failed
+
+SELECT AVG(NULLIF(YEAR('2001-01-01'),10));
+
+CREATE TABLE t1(y YEAR);
+INSERT INTO t1 VALUES(2001);
+
+SELECT AVG(NULLIF(y, 10)) FROM t1;
+
+DROP TABLE t1;

sql/item_cmpfunc.cc

@@ -3534,6 +3534,7 @@ bool Item_func_nullif::resolve_type_inner(THD *thd) {
     set_data_type_string(args[0]->max_length);
     if (agg_arg_charsets_for_comparison(cmp.cmp_collation, args, arg_count))
       return true;
+    cached_result_type = STRING_RESULT;
   }
   return false;
 }