Enable reading Mysql json type only for alter forcebb-10.3-anel-MDEV18323

- Used ALTER_RECREATE flag from lex
- Added test case
- Problem: changed .frm file with alter force HOW and WHY ?

2 files changed, 45 insertions, 2 deletions

diff --git a/mysql-test/main/mysql_json_2.test b/mysql-test/main/mysql_json_2.test
new file mode 100644
index 00000000000..e2d8395c13c
--- /dev/null
+++ b/mysql-test/main/mysql_json_2.test
@@ -0,0 +1,43 @@
+--echo #
+--echo # MDEV-18323: Convert MySQL JSON type to MariaDB TEXT in mysql_upgrade
+--echo # Test 2 (field treated as a blob):
+--echo # Can read .frm file from mysql table containg the json data,
+--echo # but is not well structured
+--echo #
+
+let $datadir=`select @@datadir`;
+
+#drop table if exists mysql_json;
+
+# Make sure you have placed `json.[frm/myd/myi]` files in `source/mysql-test/std_data/`
+--copy_file std_data/json.frm $datadir/test/mysql_json.frm
+--copy_file std_data/json.MYI $datadir/test/mysql_json.MYI
+--copy_file std_data/json.MYD $datadir/test/mysql_json.MYD
+
+--error ER_TABLE_NEEDS_REBUILD
+select * from test.mysql_json;
+--error ER_TABLE_NEEDS_REBUILD
+alter table test.mysql_json;
+alter table test.mysql_json force;
+select * from test.mysql_json;
+
+# We cannot read now
+#--error ER_TABLE_NEEDS_REBUILD
+#select * from test.mysql_json;
+
+# Create other table to test other data types
+--copy_file std_data/t1.frm $datadir/test/t1.frm
+--copy_file std_data/t1.MYI $datadir/test/t1.MYI
+--copy_file std_data/t1.MYD $datadir/test/t1.MYD
+
+# We cannot read now
+#--error ER_TABLE_NEEDS_REBUILD
+#select * from test.t1;
+
+--echo # Extend `Alter table <table_name> force ` @todo
+#alter table test.t1 force;
+# Now should be able to read data as mariadb table
+#select * from test.t1;
+
+drop table mysql_json;
+drop table t1;
diff --git a/sql/table.cc b/sql/table.cc
index 74eae05c097..00b949b4d67 100644
--- a/sql/table.cc
+++ b/sql/table.cc
@@ -1864,9 +1864,9 @@ int TABLE_SHARE::init_from_binary_frm_image(THD *thd, bool write,
           share->mysql_version < 100000 &&
           strpos[13] == (uchar) MYSQL_TYPE_VIRTUAL)
       {
-        if(!(thd->open_options & HA_OPEN_FOR_ALTER))
+        if(!(thd->lex->alter_info.flags == ALTER_RECREATE))
         {
-          // Raise an error
+          // Raise an error for every operation expect `alter table <table_name> force`
           mysql_table_to_upgrade=1;
           goto err;
         }