second and third columns meaning in tx2gene.tsv from star_salmon

[jdanaK]

Hi,
I ran the nf-core/rnaseq and DESeq2 with quant.sf files and tximport()
In the results files, I found the duplicated gene names which are seperated by '-2' such as AKAP17A / AKAP17A-2
So I checked the txi file and tx2gene file, and I identify the tx2gene.tsv file in star_salmon contains three columns.
In second column, there are some duplicated gene names separated by '-2'
I think when I create new tx2gene.tsv file by using first column and third column I can get results file with unique gene names
I'm just curious about the difference between second column and third column in tx2gene.tsv
Thank you

here is my command

sudo nextflow run nf-core/rnaseq \
--input samplesheet.csv \
--outdir outdir \
--genome GRCh38 \
-profile docker \
--pseudo_aligner salmon