pq: function unnest(unknown) is not unique

Question

Following code is working fine. But I want to define array['a', 'b', 'c', 'd', 'e'] as a variable.

rows, err :=  db.Query("select colname from (SELECT date, unnest(array['a', 'b', 'c', 'd', 'e']) AS colname, unnest(array[a, b, c, d, e]) AS thing from test1 where date='123') as tester where thing=1;")

So I try following code using github.com/lib/pq .

arr1 := []string{"a", "b", "c", "d", "e"}      
rows, err :=  db.Query("select colname from (SELECT date, unnest($1) AS colname, unnest($1) AS thing from test1 where date='123') as tester where thing=1;", pq.Array(arr1))

But getting error like "pq: function unnest(unknown) is not unique". Table structure and sample data--

test=# \d+ test1
                                Table "public.test1"
 Column |         Type          | Modifiers | Storage  | Stats target | Description 
--------+-----------------------+-----------+----------+--------------+-------------
 a      | character varying(10) |           | extended |              | 
 b      | character varying(10) |           | extended |              | 
 c      | character varying(10) |           | extended |              | 
 d      | character varying(10) |           | extended |              | 
 e      | character varying(10) |           | extended |              | 
 date   | character varying(10) |           | extended |              | 

test=# select * from test1 ;
 a | b | c | d | e | date 
---+---+---+---+---+------
 3 | 1 | 3 | 2 | 3 | 124
 3 | 3 | 2 | 2 | 1 | 125
 1 | 2 | 2 | 1 | 3 | 126
 1 | 2 | 3 | 2 | 3 | 127
 1 | 1 | 2 | 2 | 3 | 123
(5 rows)

Basically I want the column name (a,b,c,d or e) which have value '1' on any specific date.

Kuomintang

Possible duplicate of PostgreSQL 9.3: Function is not unique error – Crosscrosslet

Not expert in postgresql but in c# with standard sql i would create array of characters, then merge them with separator ", " and then use it as parameter. – Mussel

@AleksaRistic PostgreSQL has array types (which AFAIK are standard SQL even though hardly anyone supports them). – Dugout

Answer 1

I'd guess that pq.Array is giving you a PostgreSQL array in the string form so you end up with something like this:

unnest('{a,b,c,d,e}')

and PostgreSQL isn't sure how it should interpret that string, hence the complaint about unnest(unknown). You should be able to add an explicit type cast to clear things up:

unnest($1::text[])         -- PostgreSQL-specific casting syntax
unnest(cast($1 as text[])) -- Standard casting syntax

You'd end up with something like this:

rows, err :=  db.Query("select colname from (SELECT date, unnest($1::text[]) AS colname, unnest($1) AS thing from test1 where date='123') as tester where thing=1;", pq.Array(arr1))

Dugout

There is something wrong happened when variable substitute in 2nd unnest. When I uses rows, err := db.Query("select colname from (SELECT date, unnest($1::text[]) AS colname, unnest(array[a, b, c, d, e]) AS thing from test1 where date='123') as tester where thing='1';", pq.Array(arr1)) It is giving right output .But when uses following code I found no error and no output. rows, err := db.Query("select colname from (SELECT date, unnest($1::text[]) AS colname, unnest($1) AS thing from test1 where date='123') as tester where thing=1;", pq.Array(arr1)) – Kuomintang

What happens if you try the query in psql? – Dugout

test=# select colname from (SELECT date, unnest(array['a', 'b', 'c', 'd', 'e']) AS colname, unnest(array[a, b, c, d, e]) AS thing from test1 where date='123') as tester where thing='1'; colname --------- a b (2 rows) – Kuomintang

It gives 2 outputs a and b. – Kuomintang

You're going to have to include the table structure and some sample data in your question. – Dugout

Updated the description – Kuomintang

I'd recommend asking a new question with those new details and a description of you're trying to get your query to do, tag it with "sql" and "postgresql". You have an XY-problem and you're trying to solve the wrong problem (you want to solve "how do I get my desired results" rather than "how do I make this query work"). – Dugout

Ok I have created a new question . Thanks for help. – Kuomintang