Question

let’s suppose table t as the follwing:

t table:

a   b   c   d   e
a1  b1  c1  d1  e1  
a2  b2  c2  d2  e2
a3  b3  c3  d3  e3
.   .   .   .   .
.   .   .   .   .
.   .   .   .   .

this query throws an #1242 error:

SELECT CONCAT_WS( '*', (SELECT CONCAT_WS( '_', a, b, c) FROM t)) AS test

Expected result is:

test
a1_b1_c1*a2_b2_c2*a3_b3_c3*.....

What’s the best woraround?

Answer 1

The problem is that “t” has more than one row. Perhaps you want one of the following:

SELECT CONCAT_WS( '*', (SELECT CONCAT_WS( '_', a, b, c) FROM t limit 1)) AS test 

or

SELECT CONCAT_WS( '*', (SELECT max(CONCAT_WS( '_', a, b, c)) FROM t)) AS test 

Oops, I missed the expected results in the question. You want:

select group_concat(vals SEPARATOR '*' ORDER BY t.id)
from (select concat_ws('_', a, b, c) as vals
      from t
     ) t

(This assumes that there is a column called “id” for ordering the results. If not, leave out the order by clause.)