问题描述
我有一个sqlite数据库，其中包含以下格式的基本天气信息：
I have a sqlite database that contains basic weather information in the following format:
temp1 temp2 pressure humidity
22 23 1024 40
24 25 1027 45
25 26 1020 62
18 15 1019 80
如何使用 gnuplot 绘制这些数据？
how can I plot this data using gnuplot? Do I have to re-arrange the data before being able to plot it?
推荐答案
要从sqlite数据库中提取数据，您可以使用 sqlite3 命令行工具即时提取数据。这通过使用gnuplot通过使用< 来完成，它生成一个shell并使用给定shell命令的输出进行绘图。
To extract the data from your sqlite database, you can use the sqlite3 command line tool to extract the data on-the-fly. This is done with gnuplot by using a < which spawns a shell and uses the output of the given shell commands for plotting.
plot '< sqlite3 myfile.db3 "SELECT temp1, temp2, pressure, humidity FROM myTable;"' using 0:1 title 'temp1', \
'' using 0:2 title 'temp2'
这将提取每个图的所有四个字段（''文件名/ shell命令）。您还可以使用函数格式化shell命令：
This would extract all four fields for each plot ('' repeats the previous file name / shell command). You could also use function to format the shell command:
SqliteField(f) = '< sqlite3 myfile.db3 "SELECT '.f.' from myTable;"'
fields = 'temp1 temp2 pressure humidity'
plot for [f in fields] SqliteField(f) using 0:1 title f
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