于事无补

unhelpful / useless

to go / to take / sentence-final interrogative particle / variant of 於|于[yu2]

(of time or place) in; at; on / (indicating any indirect relation) to; toward; vis-à-vis; with regard to; for / (indicating a source) from; out of / (used in comparison) than / (used in the passive voice) by

matter / thing / item / work / affair / CL:件[jian4],樁|桩[zhuang1],回[hui2]

not to have / no / none / not / to lack / un- / -less

of no avail / not helping in the least

to repair / to patch / to mend / to make up for / to fill (a vacancy) / to supplement