MDEV-9167: COLUMN_CHECK fails on valid decimal data

Check now allows zero length decimals too.

(backporting Adam Chainz patch to 10.0)

mysql-test/r/dyncol.result

@@ -1858,5 +1858,20 @@ SELECT COLUMN_GET(COLUMN_CREATE(1, 0xC2A2 AS CHAR CHARACTER SET utf8), 1 AS CHAR
 a
 ¢
 #
+# MDEV-9167: COLUMN_CHECK fails on valid decimal data
+#
+SELECT COLUMN_CHECK(COLUMN_CREATE('a',0 AS DECIMAL,'b',1 AS DECIMAL));
+COLUMN_CHECK(COLUMN_CREATE('a',0 AS DECIMAL,'b',1 AS DECIMAL))
+1
+SELECT COLUMN_CHECK(COLUMN_CREATE('a',1 AS DECIMAL,'b',1 AS DECIMAL));
+COLUMN_CHECK(COLUMN_CREATE('a',1 AS DECIMAL,'b',1 AS DECIMAL))
+1
+SELECT COLUMN_JSON(COLUMN_CREATE('a',0 AS DECIMAL,'b',1 AS DECIMAL));
+COLUMN_JSON(COLUMN_CREATE('a',0 AS DECIMAL,'b',1 AS DECIMAL))
+{"a":0,"b":1}
+SELECT COLUMN_JSON(COLUMN_CREATE('a',1 AS DECIMAL,'b',1 AS DECIMAL));
+COLUMN_JSON(COLUMN_CREATE('a',1 AS DECIMAL,'b',1 AS DECIMAL))
+{"a":1,"b":1}
+#
 # end of 10.0 tests
 #

mysql-test/t/dyncol.test

@@ -908,6 +908,18 @@ SET NAMES utf8;
 SELECT COLUMN_GET(COLUMN_CREATE(1, 0xC2A2 AS CHAR CHARACTER SET latin1), 1 AS CHAR CHARACTER SET utf8) AS a;
 SELECT COLUMN_GET(COLUMN_CREATE(1, 0xC2A2 AS CHAR CHARACTER SET utf8), 1 AS CHAR CHARACTER SET utf8) AS a; 
 
+--echo #
+--echo # MDEV-9167: COLUMN_CHECK fails on valid decimal data
+--echo #
+
+SELECT COLUMN_CHECK(COLUMN_CREATE('a',0 AS DECIMAL,'b',1 AS DECIMAL));
+
+SELECT COLUMN_CHECK(COLUMN_CREATE('a',1 AS DECIMAL,'b',1 AS DECIMAL));
+
+SELECT COLUMN_JSON(COLUMN_CREATE('a',0 AS DECIMAL,'b',1 AS DECIMAL));
+
+SELECT COLUMN_JSON(COLUMN_CREATE('a',1 AS DECIMAL,'b',1 AS DECIMAL));
+
 --echo #
 --echo # end of 10.0 tests
 --echo #

mysys/ma_dyncol.c

@@ -3725,7 +3725,8 @@ mariadb_dyncol_check(DYNAMIC_COLUMN *str)
       /* It is not first entry */
       if (prev_data_offset > data_offset ||
           ((prev_type !=  DYN_COL_INT &&
-            prev_type != DYN_COL_UINT) && prev_data_offset == data_offset))
+            prev_type != DYN_COL_UINT &&
+            prev_type != DYN_COL_DECIMAL) && prev_data_offset == data_offset))
       {
         DBUG_PRINT("info", ("Field order: %u  Previous data offset: %u"
                             " >(=) Current data offset: %u",