Postgres inconsistency: array_agg(pg_typeof(...)) in pg flattens result

[nrainer-materialize]

Likely not a bug in mz but a strange behavior in pg.

Given

DROP TABLE IF EXISTS evaluation;
CREATE TABLE evaluation (row_index INT, decimal_39_8_val DECIMAL(39,8));
INSERT INTO evaluation VALUES (10, 0.99999999::DECIMAL(39,8));

SELECT array_agg(pg_typeof(decimal_39_8_val) ORDER BY row_index) FROM evaluation;

produces

• in mz: a row with a column with value ['numeric'] of type text list
• in pg: a row with a column with value '{numeric}' of type string

The behavior of pg seems a bit special here. When querying array_agg(decimal_39_8_val), pg will also return a list.

More details

Given

        x1 = self.executor.query("SELECT array_agg(pg_typeof(decimal_39_8_val) ORDER BY row_index) FROM t_dfr_vert WHERE (row_index IN (10));")
        x2 = self.executor.query("SELECT array_agg(pg_typeof(decimal_39_8_val) ORDER BY row_index) FROM t_dfr_vert WHERE (row_index IN (7,8,10));")
        x3 = self.executor.query("SELECT array_agg(decimal_39_8_val ORDER BY row_index) FROM t_dfr_vert WHERE (row_index IN (7,8,10));")
        x4 = self.executor.query("SELECT array_agg(text_val ORDER BY row_index) FROM t_dfr_vert WHERE (row_index IN (7,8,10));")

fetching from mz and

        y1 = self.pg_executor.query("SELECT array_agg(pg_typeof(decimal_39_8_val) ORDER BY row_index) FROM t_pg_vert WHERE (row_index IN (10));")
        y2 = self.pg_executor.query("SELECT array_agg(pg_typeof(decimal_39_8_val) ORDER BY row_index) FROM t_pg_vert WHERE (row_index IN (7,8, 10));")
        y3 = self.pg_executor.query("SELECT array_agg(decimal_39_8_val ORDER BY row_index) FROM t_pg_vert WHERE (row_index IN (7,8, 10));")
        y4 = self.pg_executor.query("SELECT array_agg(text_val ORDER BY row_index) FROM t_pg_vert WHERE (row_index IN (7,8, 10));")

fetching from Postgres, results are:

x1 = {tuple: 1} ([['numeric']],)
x2 = {tuple: 1} ([['numeric', 'numeric', 'numeric']],)
x3 = {tuple: 1} ([[Decimal('0.49999999'), Decimal('0.50000001'), Decimal('1.00000001')]],)
x4 = {tuple: 1} ([['ff00aa', ' mAA m\n\t ', 'a']],)
y1 = {tuple: 1} (['{numeric}'],)
y2 = {tuple: 1} (['{numeric,numeric,numeric}'],)
y3 = {tuple: 1} ([[Decimal('0.49999999'), Decimal('0.50000001'), Decimal('1.00000001')]],)
y4 = {tuple: 1} ([['ff00aa', ' mAA m\n\t ', 'a']],)

x1 differs from y1 and x2 differs from y2.