Nested Case statement type error (postgres)

Question

I have some postgres code I have created that is giving me an error:

ERROR:  CASE types character varying and numeric cannot be matched

CODE:

Answer 1

The immediate cause for the error is the data type mismatch, as the error message tells you.

In the second and third column creations is where the problem is occurring.

All possible results of a CASE expression need to share compatible data types so those must match but, obviously, don't. The manual instructs:

The data types of all the result expressions must be convertible to a single output type. See Section 10.5 for more details.

Assuming you refer to current_condition and current_ecosite - which are actually the 6th and 7th column, these need to have matching data types:

d.ecosite3
c.ecosite2
b.ecosite

and:

d.ecophase3
c.ecophase2
b.ecophase

Better query

Pending the missing table definition for boreal_mixedwood_labeled, my educated guess is you can radically simplify to this query:

SELECT a.id, a.geom, a.condition_join_1, a.condition_join_2, a.condition_join_3
     , COALESCE(d.condition3, c.condition2, b.condition) AS current_condition
     , COALESCE(d.ecosite3,   c.ecosite2,   b.ecosite)   AS current_ecosite
     , COALESCE(d.ecophase3,  c.ecophase2,  b.ecophase)  AS current_ecophase
     , COALESCE(d.consite3,   c.consite2,   b.consite)   AS current_consite
     , COALESCE(d.conphase3,  c.conphase2,  b.conphase)  AS current_conphase
FROM   current_condition a
LEFT   JOIN boreal_mixedwood_labeled b ON a.label  = b.label_join_1
LEFT   JOIN boreal_mixedwood_labeled c ON a.label2 = c.label_join_2
                                      AND b.condition = 'ERROR'
LEFT   JOIN boreal_mixedwood_labeled d ON a.label3 = d.label_join_3
                                      AND c.condition2 = 'ERROR';

Data types must still match.

How?

This is not just shorter, but probably faster, too.

Only join to boreal_mixedwood_labeled a second time if b.condition = 'ERROR' to begin with, etc.

Then you can use a simpler COALESCE expression: d.* is NULL unless we need it, same goes for c.*. The first non-null values is returned.

If some of the columns in boreal_mixedwood_labeled can be NULL the logic can break. It all depends on ... tada! ... your actual table definition. (Did I mention that enough already?). Don't forget to include it with your next question ...

Answer 2

Try eliminating the nested case. Maybe it makes a difference to the compiler for some reason:

CASE
    WHEN b.condition = 'ERROR' AND c.condition2 = 'ERROR' THEN d.condition3
    WHEN b.condition = 'ERROR' THEN c.condition2
    ELSE c.condition
END as current_condition,
...