I work as a biostatistician and I've been tasked recently with querying large databases using SQL, in addition to analysing the data. However, my programming ba

I work as a biostatistician and I've been tasked recently with querying large databases using SQL, in addition to analysing the data. However, my programming background is very limited and thus I'm sure my queries are very inefficient. Could you point me to some materials/texts about how to improve querying efficiency for SQL? If it's oriented for beginners then that would be ideal. Thanks in advance.