SQL: Difference between revisions
Created page with "SQL basics ==Common functions== See [https://www.postgresql.org/docs/16/functions-math.html Postgres math functions] and [https://www.postgresql.org/docs/current/functions-conditional.html Postgres conditional functions]. * Average * Sum * Round * [https://www.postgresql.org/docs/current/functions-conditional.html#FUNCTIONS-COALESCE-NVL-IFNULL Coalesce] - return the first non-null parameter. * [https://www.postgresql.org/docs/current/functions-conditional.html#FUNCTIO..." |
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==Common functions== | ==Common functions== | ||
See [https://www.postgresql.org/docs/16/functions-math.html Postgres math functions] | ===Math functions=== | ||
See [https://www.postgresql.org/docs/16/functions-math.html Postgres math functions] | |||
* Average | * Average | ||
* Sum | * Sum | ||
* Round | * Round | ||
===Conditional functions=== | |||
See [https://www.postgresql.org/docs/current/functions-conditional.html Postgres conditional functions]. | |||
* [https://www.postgresql.org/docs/current/functions-conditional.html#FUNCTIONS-COALESCE-NVL-IFNULL Coalesce] - return the first non-null parameter. | * [https://www.postgresql.org/docs/current/functions-conditional.html#FUNCTIONS-COALESCE-NVL-IFNULL Coalesce] - return the first non-null parameter. | ||
* [https://www.postgresql.org/docs/current/functions-conditional.html#FUNCTIONS-CASE Case] | * [https://www.postgresql.org/docs/current/functions-conditional.html#FUNCTIONS-CASE Case] | ||
Revision as of 01:43, 12 February 2024
SQL basics
Common functions
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.