\begin{filecontents*}{exampledata.dat}
category, value
1969q1,0.0281955
1969q2,0.0107725
1969q3,0.0172358
1969q4,0.022086
1970q1,0.0117069
1970q2,0.0229364
1970q3,0.0078862
1970q4,0.0059589
1971q1,0.0085788
1971q2,0.0066469
1971q3,0.0139244
1971q4,0.0160034
1972q1,0.0160311
1972q2,0.0063541
1972q3,0.0974113
1972q4,0.0781786
1973q1,0.0554917
1973q2,0.0373566
1973q3,0.0612486
1973q4,0.2361937
1974q1,0.1304208
1974q2,0.0657395
1974q3,0.0267478
1974q4,0.0076311
1975q1,0.0109018
1975q2,0.0117015
1975q3,0.0401886
1975q4,0.0198401
1976q1,0.013733
1976q2,0.0071622
1976q3,0.0212374
1976q4,0.0246715
1977q1,0.0280418
1977q2,0.0468191
1977q3,0.054814
1977q4,0.0667536
1978q1,0.0386275
1978q2,0.0188465
1978q3,0.0062134
1978q4,0.0225383
1979q1,0.0129294
1979q2,0.0046539
1979q3,0.0121312
1979q4,0.0012966
1980q1,0.0022369
1980q2,0.0018002
1980q3,0.0023382
1980q4,0.0017021
1981q1,0.0021264
1981q2,0.0014046
1981q3,0.002169
1981q4,0.0088469
1982q1,0.0030053
1982q2,0.011688
1982q3,0.0020342
1982q4,0.0055726
1983q1,0.0041684
1983q2,0.0062855
1983q3,0.0019128
1983q4,0.0040494
1984q1,0.0046358
1984q2,0.0016446
1984q3,0.0024712
1984q4,0.0027055
1985q1,0.0011616
1985q2,0.0015175
1985q3,0.0020426
1985q4,0.0026102
1986q1,0.0020301
1986q2,0.0087082
1986q3,0.005479
1986q4,0.0083939
1987q1,0.0103175
1987q2,0.0214318
1987q3,0.018462
1987q4,0.0120428
1988q1,0.0115911
1988q2,0.0033301
1988q3,0.0036929
1988q4,0.0040875
1989q1,0.0180898
1989q2,0.0061725
1989q3,0.0178756
1989q4,0.0136086
1990q1,0.0304329
1990q2,0.0375497
1990q3,0.0446735
1990q4,0.0887817
1991q1,0.050996
1991q2,0.0934737
1991q3,0.097937
1991q4,0.0612006
1992q1,0.0221894
1992q2,0.0290649
1992q3,0.0135911
1992q4,0.0157528
1993q1,0.0278771
1993q2,0.0086824
1993q3,0.0282597
1993q4,0.0193496
\end{filecontents*}

\documentclass[margin=5pt]{standalone} 
\usepackage{pgfplotstable}% loads also pgfplots
\pgfplotsset{compat=default} 
\pgfplotstableread[col sep=comma,
    display columns/0/.style=string type,
    header=true
  ]{exampledata.dat}{\loadeddata}
\begin{document} 
\begin{tikzpicture} 
  \begin{axis}[
  %xticks,
  no marks,
  smooth,
  minor tick num=4,
    xtick={0,5,...,95},% row numbers for ticks
    grid=major,
    major grid style={dotted,green!30!black},
    extra x ticks={100}, extra x tick labels={},
xticklabel={%
	\pgfmathsetmacro\rowindex{int(\tick)}% row index must be an integer
	\pgfplotstablegetelem{\rowindex}{[index]0}\of{\loadeddata}% get the string from the loaded table
	\pgfplotsretval% print the resulting ticklabel
},
xticklabel style={rotate=45,anchor=east, font=\tiny, xticklabel pos = left},]
    \addplot table [x expr=\coordindex, y index=1]\loadeddata;
  \end{axis}
\end{tikzpicture}
\end{document}