IMPLODE

Takes a column of any scalar type and returns an unbounded array. Combined with GROUP BY, this function can be used to reverse an EXPLODE operation.

Behavior Type

Immutable if the WITHIN GROUP ORDER BY clause specifies a column or set of columns that resolves to unique element values within each output array group.
Volatile otherwise because results are non-commutative.

Syntax

IMPLODE (input‑column [ USING PARAMETERS parameter=value[,...] ] ) [ within‑group‑order‑by‑clause ]

Arguments

input‑column

Column of any scalar type from which to create the array.

within‑group‑order‑by‑clause

Sorts elements within each output array group:

WITHIN GROUP (ORDER BY { column‑expression[ sort-qualifiers ] }[,...])

sort‑qualifiers:

   { ASC | DESC [ NULLS { FIRST | LAST | AUTO } ] }

WITHIN GROUP ORDER BY can consume a large amount of memory per group. To minimize memory consumption, create projections that support GROUPBY PIPELINED.

Parameters

allow_truncate

Boolean, if true truncates results when output length exceeds column size. If false (the default), the function returns an error if the output array is too large.

Even if this parameter is set to true, IMPLODE returns an error if any single array element is too large. Truncation removes elements from the output array but does not alter individual elements.

max_binary_size

The maximum binary size in bytes for the returned array. If you omit this parameter, IMPLODE uses the value of the configuration parameter DefaultArrayBinarySize.

Examples

Consider a table with the following contents:

=> SELECT * FROM filtered;
				
 position | itemprice | itemkey
----------+-----------+---------
        0 |     14.99 |     345
        0 |     27.99 |     567
        1 |     18.99 |     567
        1 |     35.99 |     345
        2 |     14.99 |     123
(5 rows)

The following query calls IMPLODE to assemble prices into arrays (grouped by keys):

=> SELECT itemkey AS key, IMPLODE(itemprice) AS prices
    FROM filtered GROUP BY itemkey ORDER BY itemkey;
 key |      prices
-----+-------------------
 123 | ["14.99"]
 345 | ["35.99","14.99"]
 567 | ["27.99","18.99"]
(3 rows)

You can modify this query by including a WITHIN GROUP ORDER BY clause, which specifies how to sort array elements within each group:

=> SELECT itemkey AS key, IMPLODE(itemprice) WITHIN GROUP (ORDER BY itemprice) AS prices 
    FROM filtered GROUP BY itemkey ORDER BY itemkey;
 key |      prices
-----+-------------------
 123 | ["14.99"]
 345 | ["14.99","35.99"]
 567 | ["18.99","27.99"]
(3 rows)