Emerge doesn't care what order the packages are given; it'll figure out the correct build order and pull in the proper dependencies. Adding the -u switch will only perform the emerge if the package is not yet installed or needs to be updated. This avoids wasting time performing an emerge on something that has already been emerged.
While harmless, it is unnecessary to explicitly include eselect-postgresql in the list as the dev-db/postgresql ebuilds declare it as a dependency. There is no "sqlite3" or "libsqlite3-dev" ebuilds, so that command would fail.
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