MDEV-7968 Virtual column set to NULL using load data infile

Don't forget to set thd->lex->unit.insert_table_with_stored_vcol
in the mysql_load(). Othewise virtual columns will not be updated.

mysql-test/suite/vcol/r/load_data.result

+create table t1 ( c1 varchar(10), c2 varchar(10), c3 int );
+insert into t1 values ("a" , "b", 1),   ("a" , "b", 2);
+create table t2 like t1 ;
+alter table t2 add column c4 bigint unsigned as (CONV(LEFT(MD5(concat(c1,c2,c3)), 16), 16, 10)) persistent unique key;
+select * into outfile 't1.csv' from t1;
+load data infile 't1.csv' into table t2 ;
+Warnings:
+Warning	1261	Row 1 doesn't contain data for all columns
+Warning	1261	Row 2 doesn't contain data for all columns
+select * from t2;
+c1	c2	c3	c4
+a	b	1	7545402351885872315
+a	b	2	6048842355806993119
+insert into t2 (c1,c2,c3) values ("a" , "b", 4);
+select * from t2;
+c1	c2	c3	c4
+a	b	1	7545402351885872315
+a	b	2	6048842355806993119
+a	b	4	15541743660496249717
+drop table t1, t2;

mysql-test/suite/vcol/t/load_data.test

+#
+# MDEV-7968 Virtual column set to NULL using load data infile
+#
+create table t1 ( c1 varchar(10), c2 varchar(10), c3 int );
+insert into t1 values ("a" , "b", 1),   ("a" , "b", 2);
+create table t2 like t1 ;
+alter table t2 add column c4 bigint unsigned as (CONV(LEFT(MD5(concat(c1,c2,c3)), 16), 16, 10)) persistent unique key;
+select * into outfile 't1.csv' from t1;
+load data infile 't1.csv' into table t2 ;
+select * from t2;
+insert into t2 (c1,c2,c3) values ("a" , "b", 4);
+select * from t2;
+drop table t1, t2;

sql/sql_load.cc

@@ -314,6 +314,18 @@ int mysql_load(THD *thd,sql_exchange *ex,TABLE_LIST *table_list,
   table->prepare_triggers_for_insert_stmt_or_event();
   table->mark_columns_needed_for_insert();
 
+  if (table->vfield)
+  {
+    for (Field **vfield_ptr= table->vfield; *vfield_ptr; vfield_ptr++)
+    {
+      if ((*vfield_ptr)->stored_in_db)
+      {
+        thd->lex->unit.insert_table_with_stored_vcol= table;
+        break;
+      }
+    }
+  }
+
   uint tot_length=0;
   bool use_blobs= 0, use_vars= 0;
   List_iterator_fast<Item> it(fields_vars);