SQL

From David's Wiki
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SQL basics


Common functions

Math functions

See Postgres math functions

  • Average
  • Sum
  • Round

Conditional functions

See Postgres conditional functions.

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.

Subqueries