关于 union 和 concat 的 SQL 查询

Question

I need to select union values from two table and also add prefix to the result values. Eg:-

select concat('Source-',id), concat('Source-',name)
from src_tbl where id IS not NULL and name IS not NULL    
UNION
select concat('Destination-',id), concat('Destination-',name)
from dstn_table where id IS not NULL and name IS not NULL  
order by name

Union and concat is working separately but wen I am combining it's not working and throwing error "that name is not found from tables on both sides of union". The column is present though

Answer 1

use alias in 1st table column name

  select concat('Source-',id) source_id,
         concat('Source-',name) name
         from src_tbl where id IS not NULL and name IS not NULL    
         UNION
  select concat('Destination-',id),
         concat('Destination-',name)
         from dstn_table where id IS not NULL and name IS not NULL  
         order by name

Answer 2

you need to define alias for column name

select concat('Source-',id) as id, concat('Source-',name) as name from src_tbl where id IS not NULL and name IS not NULL    
UNION
select concat('Destination-',id), concat('Destination-',name) from dstn_table where id IS not NULL and name IS not NULL order by name

Answer 3

The order by clause refers to the result of both queries. Add aliases there and you should be good to go:

SELECT CONCAT('Source-',id), CONCAT('Source-', name) AS name
FROM   src_tbl
WHERE  id IS NOT NULL AND name IS NOT NULL    
UNION
SELECT CONCAT('Destination-',id), CONCAT('Destination-',name) AS name
FROM   dstn_table
WHERE  id IS NOT NULL AND name IS NOT NULL  
ORDER BY name