-first_table-        -second_table-
|--var--|-value-|    |--var--|-value-|
| int   |   1   |    | float |  2.0  |
| float |  1.0  |    | char  |   b   |
| char  |   a   |    | bool  | false |
|-------|-------|    |-------|-------|

CREATE TABLE first_table ( var text, value text );
CREATE TABLE second_table ( var text, value text );

INSERT INTO first_table VALUES( 'int', '1' );
INSERT INTO first_table VALUES( 'float', '1.0' );
INSERT INTO first_table VALUES( 'char', 'a' );

INSERT INTO second_table VALUES( 'float', '2.0' );
INSERT INTO second_table VALUES( 'char', 'b' );
INSERT INTO second_table VALUES( 'bool', 'false' );

echo "SELECT var,value FROM 'first_table' WHERE var='int' UNION ALL SELECT var,value FROM 'first_table' WHERE var='float' UNION ALL SELECT var,value FROM 'first_table' WHERE var='char' UNION ALL SELECT var,value FROM 'first_table' WHERE var='bool' UNION ALL SELECT var,value FROM 'second_table' WHERE var='int' UNION ALL SELECT var,value FROM 'second_table' WHERE var='float' UNION ALL SELECT var,value FROM 'second_table' WHERE var='char' UNION ALL SELECT var,value FROM 'second_table' WHERE var='bool' ;" | sqlite3 test.db
int|1
float|1.0
char|a
float|2.0
char|b
bool|false

int|1
float|1.0
char|a
bool|N/A
int|N/A
float|2.0
char|b
bool|false

select V.var,
       coalesce(case when num=1 then F.value else S.value end, 'N/A') value
  from
   (select var from first_table
     union
    select var from second_table
   ) V
 cross join (select 1 as num union select 2) N
  left join first_table F  on N.num=1 and F.var=V.var
  left join second_table S on N.num=2 and S.var=V.var
 order by N.num, V.var desc