------柱状图---------------------------------------------
文件(table_growth.txt)内容:
月份|空间大小(GB)|记录条数
201902|11.21|1566
201903|11.91|1617
201904|13.21|2882
201905|13.65|2918
201906|170.03|2975
201907|1371.69|2462
201908|344.11|6228
201909|347.92|6399
set style data histogram
set style histogram clustered gap 1
set style fill solid 0.4 border
set datafile separator "|"
plot "D:/gnuplot_data/table_growth.txt" using 2:xticlabels(1) title
columnheader(2), '' using 3:xticlabels(1) title columnheader(3)
