feat(pg): implement QueryBuilder#updateFrom

[wms]

Documentation PR: knex/documentation#476

Introduces the updateFrom querybuilder method for PostgreSQL. This allows the creation of UPDATE <table> SET <data> FROM <name> queries, which may reference relations or CTEs outside of the target table.

I opted for creating a new QB method (updateFrom) to avoid conflict or weird interactions or unexpected changes to behaviour with the target table already being inferred from knex(table), knex.table(table), etc.

[coveralls]

coverage: 92.792% (+0.002%) from 92.79% when pulling 460f4cf on wms:pg-update-from into 8e2944d on knex:master.

[wms]

Sorry, looks like I've not fully understood how the testsuite works; its attempting to run pg-specific QB methods against other DB engines.

Is there documentation on how to correctly place my tests so that they only run against the correct DB engine(s) during CI?

[OlivierCavadenti]

It's only for PG so in tests you need to skip the test for each other non-PG db.
BY the way, we are sure only PG support update from ? Cannot be added for other DB?

if (!isPostgreSQL(knex)) {
  return this.skip();
}

[wms]

BY the way, we are sure only PG support update from ? Cannot be added for other DB?

I've not done an exhaustive search, but I know that (and am in need of support for) PostgreSQL handles this.