The sqlean-vsv extension provides virtual table for working directly with CSV files, without importing data into the database. Useful for very large datasets.
Example • Parameters • Acknowledgements • Installation and usage
For the people.csv file with the following data:
11,Diane,London
22,Grace,Berlin
33,Alice,Paris
The vsv virtual table could look like this:
.load ./vsv
create virtual table people using vsv(
filename=people.csv,
schema="create table people(id integer, name text, city text)",
columns=3,
affinity=integer
);
select * from people;
┌────┬───────┬────────┐
│ id │ name │ city │
├────┼───────┼────────┤
│ 11 │ Diane │ London │
│ 22 │ Grace │ Berlin │
│ 33 │ Alice │ Paris │
└────┴───────┴────────┘
The parameters to the vsv module (the vsv(...) part) are as follows:
filename=STRING the filename, passed to the Operating System
data=STRING alternative data
schema=STRING Alternate Schema to use
columns=N columns parsed from the VSV file
header=BOOL whether or not a header row is present
skip=N number of leading data rows to skip
rsep=STRING record separator
fsep=STRING field separator
dsep=STRING decimal separator
validatetext=BOOL validate UTF-8 encoding of text fields
affinity=AFFINITY affinity to apply to each returned value
nulls=BOOL empty fields are returned as NULL
If schema is given, then columns is also required.
filename / data nothing. You must provide one or the other
it is an error to provide both or neither
schema nothing. If not provided then one will be
generated for you from the header, or if no
header is available then autogenerated using
field names manufactured as cX where X is the
column number
columns nothing. If not specified then the number of
columns is determined by counting the fields
in the first record of the VSV file (which
will be the header row if header is specified),
the number of columns is not parsed from the
schema even if one is provided
header=no no header row in the VSV file
skip=0 do not skip any data rows in the VSV file
fsep=',' default field separator is a comma
rsep='\n' default record separator is a newline
dsep='.' default decimal separator is a point
validatetext=no do not validate text field encoding
affinity=none do not apply affinity to each returned value
nulls=off empty fields returned as zero-length
The validatetext setting will cause the validity of the field
encoding (not its contents) to be verified. It effects how
fields that are supposed to contain text will be returned to
the SQLite3 library in order to prevent invalid utf8 data from
being stored or processed as if it were valid utf8 text.
The nulls option will cause fields that do not contain anything
to return NULL rather than an empty result. Two separators
side-by-each with no intervening characters at all will be
returned as NULL if nulls is true and if nulls is false or
the contents are explicity empty ("") then a 0 length blob
(if affinity=blob) or 0 length text string.
For the affinity setting, the following processing is applied to
each value returned by the VSV virtual table:
noneno affinity is applied, all fields will be returned as text just like in the original csv module, embedded nulls will terminate the text. if validatetext is in effect then an error will be thrown if the field does not contain validly encoded text or contains embedded nullsbloball fields will be returned as blobs validatetext has no effecttextall fields will be returned as text just like in the original csv module, embedded nulls will terminate the text. if validatetext is in effect then a blob will be returned if the field does not contain validly encoded text or the field contains embedded nullsintegerif the field data looks like an integer, (regex "^ _(+|-)?\d+ _$"), then an integer will be returned as provided by the compiler and platform runtime strtoll function otherwise the field will be processed as text as defined aboverealif the field data looks like a number, (regex "^ (+|-)?(\d+.?\d|\d*.?\d+)(eE?\d+)? *$") then a double will be returned as provided by the compiler and platform runtime strtold function otherwise the field will be processed as text as defined abovenumericif the field looks like an integer (see integer above) that integer will be returned; if the field looks like a number (see real above) then the number will returned as an integer if it has no fractional part; otherwise a double will be returned
STRINGmeans a quoted stringNmeans a whole number not containing a signBOOLmeans something that evaluates as true or false. Case insensitive:yes,no,true,false,1,0. Defaults totrueAFFINITYmeans an SQLite3 type specification. Case insensitive:none,blob,text,integer,real,numeric- STRING means a quoted string. The quote character may be either a single quote or a double quote. Two quote characters in a row will be replaced with a single quote character. STRINGS do not need to be quoted if it is obvious where they begin and end (that is, they do not contain a comma). Leading and trailing spaces will be trimmed from unquoted strings.
The separator string containing exactly one character, or a valid
escape sequence. Recognized escape sequences are:
\t horizontal tab, ascii character 9 (0x09)
\n linefeed, ascii character 10 (0x0a)
\v vertical tab, ascii character 11 (0x0b)
\f form feed, ascii character 12 (0x0c)
\xhh specific byte where hh is hexadecimal
Adapted from vsv.c by Keith Medcalf.
SQLite command-line interface:
sqlite> .load ./vsv
sqlite> create virtual table temp.vsv using vsv(...);
sqlite> select * from vsv;
See How to install an extension for usage with IDE, Python, etc.
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