I like to write complex SQL statements as HEREDOCs, as removing the Perl syntax from within the SQL syntax makes for much easier reading...

i.e. it is much easier to read your CREATE TABLE statement when written as....

my $sql = <<EOF;
CREATE TABLE test_data$count(
    id PRIMARY KEY,   
    group_id NOT NULL,
    created_at NOT NULL,
    text NOT NULL) AS 
        SELECT 
            rownum,
            MOD(rownum, 5),
            TO_DATE('1-jan-07', 'dd-mon-yy') + INTERVAL '
+1' MINUTE * rownum,
            CAST ('xyz' || rownum AS VARCHAR2(50)) 
            FROM dual 
            CONNECT BY LEVEL <= $rows
EOF
[download]

This incorporates martos suggestions above, and I'll update if anyone spots any other issues.