Union in gbase8s database subquery

You can go to WHERE Clause 、FROM Within clause SELECT Statement in a subquery , And use in aggregate subqueries

UNION and UNION ALL Operator . However , Here it is GBase 8s In the version , Including... Is not supported in the following context

UNION or UNION ALL Subquery of ：

• In the definition of view

• In trigger events or Action clause

• Use FOR UPDATE Clause or use Update The cursor

Information about collection subqueries , see also Aggregate subquery . About FOR UPDATE More information about clause , see also FOR

UPDATE Clause .

Especially , The database in this version supports the inclusion of UNION Subquery of .

In the combined subquery , The database server can only resolve the column name in the scope referenced by the qualified table of the column . for example , The following query

Returns an error ：

SELECT * FROM t1 WHERE EXISTS

(SELECT a FROM t2

UNION

SELECT b FROM t3 WHERE t3.c IN

(SELECT t4.x FROM t4 WHERE t4.4 = t2.z));

Here it is , Unresolved innermost subquery t2.z, because z Occurs in table references t2 Out of the scope of reference . In the innermost sub check

Inquiry in progress , Only resolvable belongs to t4、t3 or t1 Column reference of . The scope of the table reference is extended downward through subqueries , But don't cross

UNION Operator extends to brother SELECT sentence .