feature: cross engine UNION is not supported

[davidshiz]

Is your feature request related to a problem? Please describe.

CREATE TABLE t1 (t1_int INT, t1_char CHAR(5));
CREATE TABLE t2 (t2_int INT, t2_char CHAR(5));
CREATE TABLE t3 (t3_int INT, t3_char CHAR(5))ENGINE=Innodb;
CREATE TABLE t4 (t4_int INT, t4_char CHAR(5))ENGINE=Myisam;
SELECT t1_int FROM t1 UNION SELECT t3_int FROM t3 ORDER BY t1_int;
SELECT t2_int FROM t2 UNION SELECT t4_int FROM t4 ORDER BY t2_int;

mysql> SELECT t1_int FROM t1 UNION SELECT t3_int FROM t3 ORDER BY t1_int;
ERROR 6 (HY000): The query includes syntax that is not supported by the storage engine. 
Either restructure the query with supported syntax, or enable the MySQL core::Query Path in config file to execute the query with reduced performance.
mysql>
mysql> SELECT t2_int FROM t2 UNION SELECT t4_int FROM t4 ORDER BY t2_int;
ERROR 6 (HY000): The query includes syntax that is not supported by the storage engine. 
Either restructure the query with supported syntax, or enable the MySQL core::Query Path in config file to execute the query with reduced performance.

[haitaoguan]

If the parameter tianmu_ini_allowmysqlquerypath is 1，the query includes syntax that is supported by the storage engine. but the query with reduced performance.

[hustjieke]

If the parameter tianmu_ini_allowmysqlquerypath is 1，the query includes syntax that is supported by the storage engine. but the query with reduced performance.

Is your problem solved? ping @davidshiz

[davidshiz]

It is not recommended to open the parameter(tianmu_ini_allowmysqlquerypath) @hustjieke @haitaoguan