Looking at the requirements of a project, then looking at the code, then... (╯°□°）╯︵ ┻━┻
In all seriousness though its taking requirements and implementing them. Sometimes its in very old bad code, some ok code, and sometimes some really good code. The hard part is understanding the big picture when there are thousands of tables, separate systems that need to talk to each other and with almost none of it documented.
THIS. Exactly my job real description.
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