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56 lines
4.4 KiB
ReStructuredText
56 lines
4.4 KiB
ReStructuredText
TabSeparated
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------------
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In TabSeparated format, data is written by row. Each row contains values separated by tabs. Each value is follow by a tab, except the last value in the row, which is followed by a line break. Strictly Unix line breaks are assumed everywhere. The last row also must contain a line break at the end. Values are written in text format, without enclosing quotation marks, and with special characters escaped.
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Numbers are written in decimal form. Numbers may contain an extra "+" symbol at the beginning (but it is not recorded during an output). Non-negative numbers can't contain the negative sign. When parsing, it is allowed to parse an empty string as a zero, or (for signed types) a string consisting of just a minus sign as a zero. Numbers that do not fit into the corresponding data type may be parsed as a different number, without an error message.
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Floating-point numbers are formatted in decimal form. The dot is used as the decimal separator. Exponential entries are supported, as are 'inf', '+inf', '-inf', and 'nan'. An entry of floating-point numbers may begin or end with a decimal point.
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During formatting, accuracy may be lost on floating-point numbers.
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During parsing, a result is not necessarily the nearest machine-representable number.
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Dates are formatted in YYYY-MM-DD format and parsed in the same format, but with any characters as separators.
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DateTimes are formatted in the format YYYY-MM-DD hh:mm:ss and parsed in the same format, but with any characters as separators.
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This all occurs in the system time zone at the time the client or server starts (depending on which one formats data). For DateTimes, daylight saving time is not specified. So if a dump has times during daylight saving time, the dump does not unequivocally match the data, and parsing will select one of the two times.
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During a parsing operation, incorrect dates and dates with times can be parsed with natural overflow or as null dates and times, without an error message.
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As an exception, parsing DateTime is also supported in Unix timestamp format, if it consists of exactly 10 decimal digits. The result is not time zone-dependent. The formats ``YYYY-MM-DD hh:mm:ss`` and ``NNNNNNNNNN`` are differentiated automatically.
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Strings are parsed and formatted with backslash-escaped special characters. The following escape sequences are used while formatting: ``\b``, ``\f``, ``\r``, ``\n``, ``\t``, ``\0``, ``\'``, and ``\\``. For parsing, also supported \a, \v and \xHH (hex escape sequence) and any sequences of the type \c where c is any character (these sequences are converted to c). This means that parsing supports formats where a line break can be written as \n or as \ and a line break. For example, the string 'Hello world' with a line break between the words instead of a space can be retrieved in any of the following variations:
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::
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Hello\nworld
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Hello\
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world
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The second variant is supported because MySQL uses it when writing tab-separated dumps.
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Only a small set of symbols are escaped. You can easily stumble onto a string value that your terminal will ruin in output.
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Minimum set of symbols that you must escape in TabSeparated format is tab, newline (LF) and backslash.
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Arrays are formatted as a list of comma-separated values in square brackets. Number items in the array are formatted as normally, but dates, dates with times, and strings are formatted in single quotes with the same escaping rules as above.
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The TabSeparated format is convenient for processing data using custom programs and scripts. It is used by default in the HTTP interface, and in the command-line client's batch mode. This format also allows transferring data between different DBMSs. For example, you can get a dump from MySQL and upload it to ClickHouse, or vice versa.
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The TabSeparated format supports outputting total values (when using WITH TOTALS) and extreme values (when 'extremes' is set to 1). In these cases, the total values and extremes are output after the main data. The main result, total values, and extremes are separated from each other by an empty line. Example:
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``SELECT EventDate, count() AS c FROM test.hits GROUP BY EventDate WITH TOTALS ORDER BY EventDate FORMAT TabSeparated``
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.. code-block:: sql
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2014-03-17 1406958
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2014-03-18 1383658
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2014-03-19 1405797
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2014-03-20 1353623
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2014-03-21 1245779
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2014-03-22 1031592
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2014-03-23 1046491
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0000-00-00 8873898
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2014-03-17 1031592
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2014-03-23 1406958
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It's also available as ``TSV``.
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