[Bug] Query external table with UNION get incomplete result.

[morningman]

Describe the bug
How to reproduce:

CREATE EXTERNAL TABLE db1.tbl1
(
k1 INT
)
ENGINE=mysql
PROPERTIES
(
"host" = "xxxx",
"port" = "8777",
"user" = "root",
"password" = "xxx",
"database" = "cmytest",
"table" = "tbl1"
);

CREATE EXTERNAL TABLE db1.tbl2
(
k1 INT
)
ENGINE=mysql
PROPERTIES
(
"host" = "xxxx",
"port" = "8777",
"user" = "root",
"password" = "xxxx",
"database" = "cmytest",
"table" = "tbl1"
);

CREATE EXTERNAL TABLE db1.tbl3
(
k1 INT
)
ENGINE=mysql
PROPERTIES
(
"host" = "xxxx",
"port" = "8777",
"user" = "root",
"password" = "xxxx",
"database" = "cmytest",
"table" = "tbl1"
);

create view v1 as select * from tbl1 union all select * from tbl2 union all select * from tbl3;

And query like:

select count(*) from v1;

if there are more than 1024 rows in mysql table, the query will return less than 3000.

• Version [0.13.11]