SQL

SQL basics

Common functions

Math functions

See Postgres math functions

• Average
• Sum
• Round

Conditional functions

See Postgres conditional functions.

• Coalesce - return the first non-null parameter.
• Case

Joins

Joins merge two tables into a single table. You can think of this like an outer product, applying some conditions to subset from every possible combination of rows from the two tables.

• Inner join - creates rows only if keys match between the rows
• Left join - keep all rows from the left table
• Right join - keep all rows from the right table
• Outer join - keep rows from both tables.