SQL
Read a query someone else wrote, and write one that answers the question you were asked.
For anyone who needs to get an answer out of a database — analysts, developers, students. No prior SQL needed. The examples use standard syntax that works in PostgreSQL, MySQL and SQLite alike unless a difference is called out.
Start: SELECT and WHERE: asking for rows- SELECT and WHERE: asking for rowsA query names the columns, the table, and the test each row must pass.3 min
- JOIN: rows from more than one tableA join matches rows across tables; which join you pick decides what happens when there is no match.3 min
- GROUP BY: one row per groupGrouping collapses rows, and every column you select has to survive the collapse.2 min
- Changing data without regretUPDATE and DELETE do exactly what you asked, including when you asked for everything.2 min