SELECT  url_host,
        COUNT(CASE WHEN post_ID = -1 THEN 1 ELSE NULL END) Negative_One,
        COUNT(CASE WHEN post_ID = 0 THEN 1 ELSE NULL END) Zero,
        COUNT(CASE WHEN post_ID > 0 THEN 1 ELSE NULL END) Greater_Zero
FROM tableName
GROUP BY url_host

SELECT url_host,
    SUM(CASE WHEN post_id = -1 THEN 1 ELSE 0 END) as post_id_minus1,
    SUM(CASE WHEN post_id = 0 THEN 1 ELSE 0 END) as post_id_0,
    etc...
FROM    YOUR_TABLE
GROUP BY url_host