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Concatenating the nested arrays {{1,2}} and {{3,4}} is no problem at all:

SELECT array_cat(
           ARRAY[ARRAY[1,2]]
         , ARRAY[ARRAY[3,4]]
       )

   array_cat   
---------------
 {{1,2},{3,4}}

But how to concatenate {{1,2}} and {{3}} in order to get {{1,2},{3}}?

SELECT array_cat(
           ARRAY[ARRAY[1,2]]
         , ARRAY[ARRAY[3]]
       )
psql: …: ERROR:  cannot concatenate incompatible arrays
DETAIL:  Arrays with differing element dimensions are not compatible
         for concatenation.
share|improve this question
    
What structure do you expect for the final array? {{1,2},{3}} ? –  Tony May 28 at 16:34
    
I've just updated the question. –  user3684490 May 28 at 16:35

1 Answer 1

up vote 0 down vote accepted

This is impossible in PostgreSQL. Multi-dimensional arrays must have the same number of element dimensions, just as the error message informs. Per documentation:

Multidimensional arrays must have matching extents for each dimension. A mismatch causes an error.

You might want to pad with NULL or some other dummy value ...

share|improve this answer
    
I've already feared that. Seems like I have to look for another approach for my application. –  user3684490 May 28 at 16:41

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