Key-Value Map-Reduce SEO

SELECT

EBNF

SELECT ('*' | column_family_name [',' column_family_name]*)

  FROM table_name

  [where_clause]

  [options_spec]



where_clause:

    WHERE where_predicate [AND where_predicate ...]



where_predicate:

  cell_predicate

  | row_predicate

  | timestamp_predicate



relop: '=' | '<' | '<=' | '>' | '>=' | '=^'



cell_spec: row ',' column



cell_predicate:

  [cell_spec relop] CELL relop cell_spec

  | '(' [cell_spec relop] CELL relop cell_spec

        (OR [cell_spec relop] CELL relop cell_spec)* ')'



row_predicate:

  [row_key relop] ROW relop row_key

  | '(' [row_key relop] ROW relop row_key

          (OR [row_key relop] ROW relop row_key)* ')'



timestamp_predicate:

  [timestamp relop] TIMESTAMP relop timestamp



options_spec:

  (REVS revision_count

  | LIMIT row_count

  | INTO FILE filename[.gz]

  | DISPLAY_TIMESTAMPS

  | KEYS_ONLY

  | NOESCAPE

  | RETURN_DELETES)*



timestamp:

  'YYYY-MM-DD HH:MM:SS[.nanoseconds]'

Description

The parser only accepts a single timestamp predicate. The ‘=^’ operator is the “starts with” operator. It will return all rows that have the same prefix as the operand.

Options

REVS revision_count

Each cell in a Hypertable table can have multiple timestamped revisions. By default all revisions of a cell are returned by the

statement. The

option allows control over the number of cell revisions returned. The cell revisions are stored in reverse-chronological order, so

will return the most recent version of the cell.

LIMIT row_count

Limits the number of rows returned by the

statement to

.

INTO FILE filename[.gz]

The result of a

command is displayed to standard output by default. The

option allows the output to get redirected to a file. If the file name specified ends in a

extension, then the output is compressed with gzip before it is written to the file. The first line of the output, when using the

option, is a header line, which will take one of the two following formats. The second format will be output if the

option is supplied.

 #row '\t' column '\t' value



 #timestamp '\t' row '\t' column '\t' value

DISPLAY_TIMESTAMPS

The

command displays one cell per line of output. Each line contains three tab delimited fields, row, column, and value. The

option causes the cell timestamp to be included in the output as well. When this option is used, each output line will contain four tab delimited fields in the following order:

 timestamp, row, column, value

KEYS_ONLY

The

option suppresses the output of the value. It is somewhat efficient because the option is processed by the RangeServers and not by the client. The value data is not transferred back to the client, only the key data.

NOESCAPE

The output format of a

command comprises tab delimited lines, one cell per line, which is suitable for input to the

command. However, if the value portion of the cell contains either newline or tab characters, then it will confuse the

input parser. To prevent this from happening, newline and tab characters are converted into two character escape sequences, described in the following table.

 '\' 'n'

 '\' 't'

The

option turns off this escaping mechanism.

RETURN_DELETES

The

option is used internally for debugging. When data is deleted from a table, the data is not actually deleted right away. A delete key will get inserted into the database and the delete will get processed and applied during subsequent scans. The

option will return the delete keys in addition to the normal cell keys and values. This option can be useful when used in conjuction with the

option to understand how the delete mechanism works.

Examples

SELECT * FROM test WHERE ('a' <= ROW <= 'e') and

                         '2008-07-28 00:00:02' < TIMESTAMP < '2008-07-28 00:00:07';

SELECT * FROM test WHERE ROW =^ 'b';

SELECT * FROM test WHERE (ROW = 'a' or ROW = 'c' or ROW = 'g');

SELECT * FROM test WHERE ('a' < ROW <= 'c' or ROW = 'g' or ROW = 'c');

SELECT * FROM test WHERE (ROW < 'c' or ROW > 'd');

SELECT * FROM test WHERE (ROW < 'b' or ROW =^ 'b');

SELECT * FROM test WHERE "farm","tag:abaca" < CELL <= "had","tag:abacinate";

SELECT * FROM test WHERE "farm","tag:abaca" <= CELL <= "had","tag:abacinate";

SELECT * FROM test WHERE CELL = "foo","tag:adactylism";

SELECT * FROM test WHERE CELL =^ "foo","tag:ac";

SELECT * FROM test WHERE CELL =^ "foo","tag:a";

SELECT * FROM test WHERE CELL > "old","tag:abacate";

SELECT * FROM test WHERE CELL >= "old","tag:abacate";

SELECT * FROM test WHERE "old","tag:foo" < CELL >= "old","tag:abacate";

SELECT * FROM test WHERE ( CELL = "maui","tag:abaisance" OR

                           CELL = "foo","tag:adage" OR

                           CELL = "cow","tag:Ab" OR

                           CELL =^ "foo","tag:acya");