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Last tested: Feb 7, 2018
You may be getting this error because Looker's SQL Runner is unable to return Arrays in the query results. If the column is a type Array and is in the Select statement, users may encounter the error Java::JavaLang::ClassCastException:
When using arrays, it may be necessary to UNNEST or convert Array to String. A couple functions that can solve for this error are:
UNNEST operator takes an
ARRAY and returns a table, with one row for each element in the
ARRAY. You can also use
UNNEST outside of the
FROM clause with the IN operator.
Converting Arrays to Strings
ARRAY_TO_STRING() function allows you to convert an
ARRAY<STRING> to a single
STRING value or an
ARRAY<BYTES> to a single
BYTES value where the resulting value is the ordered concatenation of the array elements.
See Google Documentation here for more information: