In relational databases, it is possible to request that the database engine executes a function when an event is about to take place within a table. The events that can trigger such a function are INSERT, UPDATE and DELETE.
In the case of triggers called before these operations, database engines give us an additional power: the power to intervene, and possibly prevent the operation from taking place.
This is the core concept of this lesson.
In the SQL snippet below, you see custom aggregates that are similar to first_value/last_value but which ignore NULL values, making them more useful in my opinion.
-- "s" stands for state, "v" stands for value, "sf" stands for state (transition) function
-- since these are defined as 'strict', "s" is the previous, while "v" is the next, non-null
-- value in the defined window.
create or replace function sf_first_value_ignore_nulls(s anyelement, v anyelement)
| function numBusesToDestination( | |
| routes: number[][], | |
| source: number, | |
| target: number | |
| ): number { | |
| // 1 <= routes.length (n) <= 500. | |
| // 1 <= routes[i].length (m) <= 10^5 | |
| // construct a hashmap for stops | O(m x n) |
| #!/usr/bin/env bash | |
| # The public IP address or the Dynamic DNS hostname of the | |
| # proxmox host, which can be resolved to a public IP address | |
| PROXMOX_HOST=host.dyndns.org | |
| # A single TCP port that is used for initiating a connection | |
| PROXMOX_TCP_PORT=2222 | |
| # A range of UDP ports that can be used for each Mosh session | |
| PROXMOX_UDP_PORTS=60001:60008 |