Structured Query Language [SQL] - a common language supporting data INSERT, UPDATE (DELETE) and SELECT for relational databases.
I quickly learned SQL on the job (at Squirrel Internet, May 1999) as more of our clients' websites required dynamic content pulled from databases. Early examples were on the Queensland Bed & Breakfast Association [QBBA] site, using SQL queries to an ODBC database (through Cold Fusion), and the RSL National Historial Database using SQL queries through PERL to a MySQL database.
I have experience in designing and working with complex database structures from my time at Jumbomall (Sep 1999 - Jun 2000). I have developed both with web-based administration tools (for QBBA and Jumbomall), as well as the public search/selection (dynamic content) pages.