Best of Google homepage logos over the years

Google modifies their home page by including birthdays of some major personalities around the world or major events. Here are some of the best, unique and presented in more than one country. The list below is not any particular order.

2009.05.20 - Charles Darwin Birthday

2009.11.13 - Water on Moon found

2009.10.02 - Mahatma Gandhi

Introduction and using MySQL Explain

Like in any database query optimization is critical for MySQL data warehouse environment and having a better understanding of the "Explain plan" helps the database application developer avoiding issues with query  performance. Also, DBAs will like your queries and they would be more than happy to help you optimize them.

MySQL's "Explain" statement provides details on query parsing and execution steps and outputs 10 fields -
id, select_type, table, type, possible_keys, key, key_len, ref, rows and Extra columns.

You run the statement by issuing

explain <sql query> #-- Insert your query between < and >. 

Shown below is the Toad's output of explain plan of a self-joined table's query with where clause. The table has around 20million rows. The query took less than 0.6seconds to index through ~70K rows and with "const" and a func (date_add function) to compare between one days data to its previous day data.

SELECT a.ad_date, a.unit_id, a.max_cpc, 
               SUM(coalesce(a.max_cpc, a.max_cpc) - coalesce(b.max_cpc, a.max_cpc)) diff_cpc
       FROM  sem_kw_summary a
       LEFT JOIN  sem_kw_summary b
           ON  date_add(a.ad_date, INTERVAL -1 day)  = b.ad_date
           AND a.unit_id = b.unit_id
       WHERE date_add(CURRENT_DATE, INTERVAL -1 day) = a.ad_date
         AND a.engine = 'google'
       GROUP BY a.ad_date,  a.unit_id