TDengine data loss issue

Question

The issue is as follows, there are two clients

client 1:

taos> create table stb(ts timestamp, c1 int, c2 float) tags(t1 int);
Query OK, 0 of 0 row(s) in database (0.002777s)

taos>  insert into t1 using stb tags(1) values(now, 1, 1.2);
Query OK, 1 of 1 row(s) in database (0.011575s)

taos> select * from stb;
           ts            |     c1      |          c2          |     t1      |
=============================================================================
 2021-09-29 23:07:03.665 |           1 |              1.20000 |           1 |
Query OK, 1 row(s) in set (0.002033s)

client 2:

taos> select * from stb;
           ts            |     c1      |          c2          |     t1      |
=============================================================================
 2021-09-29 23:07:03.665 |           1 |              1.20000 |           1 |
Query OK, 1 row(s) in set (0.002254s)

Everything looks good for now, but after following steps

client 1:

taos> alter table stb drop column c2;
Query OK, 0 of 0 row(s) in database (0.004846s)

taos> alter table stb add column c2 double;
Query OK, 0 of 0 row(s) in database (0.003483s)

client 2:

taos> insert into t1 values(now, 2, 2.2);
Query OK, 1 of 1 row(s) in database (0.001591s)

Now execute below query in both clients:

client 1:

taos> select * from t1;
           ts            |     c1      |            c2             |
====================================================================
 2021-09-29 23:07:03.665 |           1 |                      NULL |
 2021-09-29 23:09:37.872 |           2 |                      NULL |
Query OK, 2 row(s) in set (0.002334s)

client 2:

taos> select * from t1;
           ts            |     c1      |            c2             |
====================================================================
 2021-09-29 23:07:03.665 |           1 |               1.200000000 |
 2021-09-29 23:09:37.872 |           2 |               2.200000000 |
Query OK, 2 row(s) in set (0.002121s)

Why the same query in different clients has different results? Is there a data loss issue in this scenario?

Answer 1

Quick answer for this question is yes since there is a known TDengine design issue in TDengine 2.x. So it is not recommended for user to delete a float column and add back a double column with the same name.