The following query produces a(nother) query that will get the value of count(*) for every table, from every schema, listed in information_schema.tables. The entire result of the query shown here - all rows taken together - comprise a valid SQL statement ending in a semicolon - no dangling 'union'. The dangling union is avoided by use of a union in the query below.
select concat('select "', table_schema, '.', table_name, '" as `schema.table`,
count(*)
from ', table_schema, '.', table_name, ' union ') as 'Query Row'
from information_schema.tables
union
select '(select null, null limit 0);';