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Overview
Artifact ID: | 6301be65aadd141a627a41499f355e3f12e9d8fb |
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Page Name: | Virtual Tables (misc) |
Date: | 2018-08-22 08:55:52 |
Original User: | sandro |
Parent: | c14fe1d90e3238e66d8c5e1b1690a50c316e8d30 (diff) |
Next | b909a6392335b23bfdfa8458f2ea91059b4ced60 |
Content
VirtualShape
The VirtualShape Interface allows to directly access an external ShapeFile by using standard Spatial SQL queries.Syntax for creating a VirtualShape Table:
SELECT CREATE VIRTUAL TABLE my_table USING VirtualShape ( shp_path , charset_encoding , srid ); SELECT CREATE VIRTUAL TABLE my_table USING VirtualShape ( shp_path , charset_encoding , srid , text_dates ); SELECT CREATE VIRTUAL TABLE my_table USING VirtualShape ( shp_path , charset_encoding , srid , text_dates , colname_case );Supported arguments and their interpretation:
- shp_path (mandatory): the relative or absolute pathname leading to the external Shapefile.
- Note: any Shapefile requires at least three individual members sharing the same base name but with different suffixes (*.shp, *.shx and *.dbf).
All suffixes will be automatically handled by VirtualShape, and consequently the shp_path argument must not specify any prefix, just the bare base path must be passed.
- Note: any Shapefile requires at least three individual members sharing the same base name but with different suffixes (*.shp, *.shx and *.dbf).
- charset_encoding (mandatory): canonical name of the charset encoding adopted by the DBF member.
- Examples of valid names are: ASCII, UTF-8, CP850, ISO-8849-1
- You can check the full list of supported charset encodings from here.
- srid (mandatory): the SRID value of all Geometries within the Shapefile.
- Examples of valid SRID values are: 4326, 3003, 32632
- text_dates (optional): this is a BOOLEAN flag:
- if set to 0 (FALSE) all fields of the DATE type will be represented as julian dates
- if set to any other integer value (TRUE) all fields of the DATE type will be represented as Text Strings as e.g. 2018-08-21
- if not explicitly specified, TRUE will always be assumed (default setting).
- colname_case (optional): this argument specifies if all column names should be considered uppercase or lowercase.
Valid settings are:- uppercase or upper: all column names will be fully capitalized.
- lowercase or lower: all column names will be full lowercase.
- samecase or same: all column names will be exactly preserved as they are defined into the DBF memeber.
- if not specified, or if any other definition definition is found, lowercase will always be assumed (default setting).
Note: quoting or not any Text String when it appears as a Virtual Table argument has absolutely no effect.
SELECT CREATE VIRTUAL TABLE my_table USING VirtualShape( /home/sandro/myshp , CP1252 , 3003 , 1 , lower ); or SELECT CREATE VIRTUAL TABLE my_table USING VirtualShape( '/home/sandro/myshp' , 'CP1252' , 3003 , 1 , 'lower' );Both notations will produce exactly the same identical result. |
Best practices and known limitations
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VirtualDBF
The VirtualDBF Interface allows to directly access an external DBF table by using standard Spatial SQL queries.Syntax for creating a VirtualDbf Table:
SELECT CREATE VIRTUAL TABLE my_table USING VirtualDbf ( dbf_path , charset_encoding ); SELECT CREATE VIRTUAL TABLE my_table USING VirtualDbf ( dbf_path , charset_encoding , text_dates ); SELECT CREATE VIRTUAL TABLE my_table USING VirtualDbf ( dbf_path , charset_encoding , text_dates , colname_case );Supported arguments and their interpretation:
- dbf_path (mandatory): the relative or absolute pathname leading to the external DBF file.
- Note: the full pathname must be passed, including the final *.dbf suffix.
- charset_encoding (mandatory): canonical name of the charset encoding adopted by the DBF member.
- Examples of valid names are: ASCII, UTF-8, CP850, ISO-8849-1
- You can check the full list of supported charset encodings from here.
- text_dates (optional): this is a BOOLEAN flag:
- if set to 0 (FALSE) all fields of the DATE type will be represented as julian dates
- if set to any other integer value (TRUE) all fields of the DATE type will be represented as Text Strings as e.g. 2018-08-21
- if not explicitly specified, TRUE will always be assumed (default setting).
- colname_case (optional): this argument specifies if all column names should be considered uppercase or lowercase.
Valid settings are:- uppercase or upper: all column names will be fully capitalized.
- lowercase or lower: all column names will be full lowercase.
- samecase or same: all column names will be exactly preserved as they are defined into the DBF memeber.
- if not specified, or if any other definition definition is found, lowercase will always be assumed (default setting).
Note: quoting or not any Text String when it appears as a Virtual Table argument has absolutely no effect.
SELECT CREATE VIRTUAL TABLE my_table USING VirtualDbf( /home/sandro/myshp , CP1252 , 1 , lower ); or SELECT CREATE VIRTUAL TABLE my_table USING VirtualDbf( '/home/sandro/myshp' , 'CP1252' , 1 , 'lower' );Both notations will produce exactly the same identical result. |
Best practices and known limitations
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VirtualText
The VirtualText Interface allows to directly access an external Text file by using standard Spatial SQL queries.The Text File is expected to contain a properly formatted Table accordingly to some Delimiter-Separated-Values format (comma separated values *.csv, tab separated values *.txt and alike).
Syntax for creating a VirtualText Table:
SELECT CREATE VIRTUAL TABLE my_table USING VirtualText ( textfile_path , charset_encoding ); SELECT CREATE VIRTUAL TABLE my_table USING VirtualText ( textfile_path , charset_encoding , first_row_as_titles ); SELECT CREATE VIRTUAL TABLE my_table USING VirtualText ( textfile_path , charset_encoding , first_row_as_titles , decimal_separator ); SELECT CREATE VIRTUAL TABLE my_table USING VirtualText ( textfile_path , charset_encoding , first_row_as_titles , decimal_separator , text_separator ); SELECT CREATE VIRTUAL TABLE my_table USING VirtualText ( textfile_path , charset_encoding , first_row_as_titles , decimal_separator , text_separator , field_separator );Supported arguments and their interpretation:
- textfile_path (mandatory): the relative or absolute pathname leading to the external Text file.
- Note: the full pathname must be passed, including an eventual final suffix (*.txt, *.csv and alike).
- charset_encoding (mandatory): canonical name of the charset encoding adopted by the Text file.
- Examples of valid names are: ASCII, UTF-8, CP850, ISO-8849-1
- You can check the full list of supported charset encodings from here.
- first_row_as_titles (optional): this is a BOOLEAN flag:
- if set to 0 (FALSE) all column names will be automatically set by using a progressive sequence.
- if set to any other integer value (TRUE) all column names will by expected to be defined in the very first row of the Text file.
- if not explicitly specified, TRUE will always be assumed (default setting).
- decimal_separator (optional): the character acting as a separator between the integer and decimal parts of a number.
Valid values are any printable character or the special mnemonic notations POINT or COMMA.
If not explicitly specified POINT will always be assumed (default setting) - text_separator (optional): the character acting as a string delimiter.
Valid values are any printable character or the special mnemonic notations SINGLEQUOTE, DOUBLEQUOTE or NONE.
If not explicitly specified DOUBLEQUOTE will always be assumed (default setting) - field_separator (optional): the character acting as a delimiter between consecutive fields.
Valid values are any printable character or the special mnemonic notations TAB.
If not explicitly specified TAB will always be assumed (default setting)
Note: quoting or not any Text String when it appears as a Virtual Table argument has absolutely no effect.
SELECT CREATE VIRTUAL TABLE my_table USING VirtualText( /home/sandro/myfile.txt , CP1252 , 1 , POINT , NONE , TAB ); or SELECT CREATE VIRTUAL TABLE my_table USING VirtualText( '/home/sandro/myfile.txt' , 'CP1252' , 1 , 'POINT' , 'NONE' , 'TAB' );Both notations will produce exactly the same identical result. |
Best practices and known limitations
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