LaTeX - left align a table (ie not centred) from the preamble?

I'm making a document in LaTeX, but I can only change the preamble of the document. Inside this document I have tables, made 开发者_如何转开发with the longtable environment. By default LaTeX centres each table in the middle of the page. Is there anyway to make the tables be left aligned, given that I can only change the preamble?

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From the documentation

The optional argument of longtable controls the horizontal alignment of the table. The possible options are [c], [r] and [l], for centring, right and left adjustment, respectively. Normally centring is the default, but this document specifies

  \setlength\LTleft\parindent
  \setlength\LTright\fill

in the preamble, which means that the tables are set flush left, but indented by the usual paragraph indentation.