Kohärentes Verhalten

Kurz nochmal zum Unterschied monochromatisches und kohärentes Licht: Positionieren wird vor einer Glühlampe einen Farbfilter, der nur noch elektromagnetische Strahlung einer Wellenlänge durchlässt, so erhalten wir monochromatisches Licht. Das “einfarbige” Licht ist nun zeitlich kohärent (gleiche Wellenlänge), die Ausbreitung der Wellenlängen im Raum hat aber noch keine feste Phasenbeziehung. Daher gilt, dass kohärentes Licht auch monochromatisches Licht darstellt, während monochromatisches Licht nicht immer kohärent sein muss. Dies kann man aber bei monochromatischen Licht auch erreichen, beispielsweise, indem man eine Blende vor den Farbfilter positioniert und somit die Wellenzüge (der ausbreitenden Wellen) in Phase bringt.

A reader should report an error if a field-count word is neither -1 nor the expected number of columns. This provides an extra check against somehow getting out of sync with the data.

Im Fach Physik wird kohärentes Licht noch enger definiert. Kohärentes Licht ist eine elektromagnetische Strahlung, wobei die Wellenfronten eine festen räumlichen und zeitlichen Zusammenhang aufweisen. Die räumliche Kohärenz liegt vor, wenn alle Wellenfronten die gleiche Ausbreitung haben (feste Phasenbeziehung), während zeitliche Kohärenz vorliegt, wenn alle “Wellenfronten” die gleiche Wellenlänge haben. Erst dann wird in der Physik von kohärentem Licht gesprochen.

Kohärentsein

The binary file format consists of a file header, zero or more tuples containing the row data, and a file trailer. Headers and data are in network byte order.

Specify the amount of messages emitted by a COPY command: default or verbose. If verbose is specified, additional messages are emitted during processing.

Presently, COPY TO will never emit an octal or hex-digits backslash sequence, but it does use the other sequences listed above for those control characters.

To determine the appropriate binary format for the actual tuple data you should consult the PostgreSQL source, in particular the *send and *recv functions for each column's data type (typically these functions are found in the src/backend/utils/adt/ directory of the source distribution).

Each tuple begins with a 16-bit integer count of the number of fields in the tuple. (Presently, all tuples in a table will have the same count, but that might not always be true.) Then, repeated for each field in the tuple, there is a 32-bit length word followed by that many bytes of field data. (The length word does not include itself, and can be zero.) As a special case, -1 indicates a NULL field value. No value bytes follow in the NULL case.

Presently, all data values in a binary-format file are assumed to be in binary format (format code one). It is anticipated that a future extension might add a header field that allows per-column format codes to be specified.

A command to execute. In COPY FROM, the input is read from standard output of the command, and in COPY TO, the output is written to the standard input of the command.

Wie eingangs erwähnt, handelt es sich bei kohärentem Licht um eine elektromagnetische Strahlung mit einer bestimmten Wellenlänge und einer bestimmten Phasenverschiebung. Darin besteht auch der Unterschied zwischen monochromatischem Licht und kohärentem Licht. Dies lässt sich auch durch das Fremdwort “kohärent” ableiten. Die Bezeichnung “kohärent” leitet sich aus dem Lateinischen und bedeutet sinngemäß “zusammenhängend”. Bei einem kohärenten Licht liegt also ein “Zusammenhang” zwischen den einzelnen Wellenfronten bzw. Wellenzügen vor (=> feste Phasenverschiebung)

The following is the same data, output in binary format. The data is shown after filtering through the Unix utility od -c. The table has three columns; the first has type char(2), the second has type text, and the third has type integer. All the rows have a null value in the third column.

This design allows for both backwards-compatible header additions (add header extension chunks, or set low-order flag bits) and non-backwards-compatible changes (set high-order flag bits to signal such changes, and add supporting data to the extension area if needed).

Licht, so wie wir es von der Sonne oder Glühlampen kennen, sendet keine kohärente Strahlung aus. Dies liegt daran, dass diese Lichtquellen Licht in alle Richtungen aussenden und nicht nur Licht einer Wellenlänge aussenden, sondern vieler Wellenlängen. Die bekannteste Quelle für kohärentes Licht ist der Laser. Jede “Laserstrahlung” weist eine zeitliche und räumliche Kohärenz auf.

A SELECT, VALUES, INSERT, UPDATE, DELETE, or MERGE command whose results are to be copied. Note that parentheses are required around the query.

Executing a command with PROGRAM might be restricted by the operating system's access control mechanisms, such as SELinux.

The specified null string is sent by COPY TO without adding any backslashes; conversely, COPY FROM matches the input against the null string before removing backslashes. Therefore, a null string such as \N cannot be confused with the actual data value \N (which would be represented as \\N).

KohärentEnglisch

Do not confuse COPY with the psql instruction \copy. \copy invokes COPY FROM STDIN or COPY TO STDOUT, and then fetches/stores the data in a file accessible to the psql client. Thus, file accessibility and access rights depend on the client rather than the server when \copy is used.

FORCE_NULL and FORCE_NOT_NULL can be used simultaneously on the same column. This results in converting quoted null strings to null values and unquoted null strings to empty strings.

Match the specified columns' values against the null string, even if it has been quoted, and if a match is found set the value to NULL. In the default case where the null string is empty, this converts a quoted empty string into NULL. If * is specified, the option will be applied to all columns. This option is allowed only in COPY FROM, and only when using CSV format.

psql will print this command tag only if the command was not COPY ... TO STDOUT, or the equivalent psql meta-command \copy ... to stdout. This is to prevent confusing the command tag with the data that was just printed.

Das Licht von einer Glühbirne ist nicht kohärent, weil die Lichtwellen in zufälligen Phasenbeziehungen zueinander emittiert werden.

The file header consists of 15 bytes of fixed fields, followed by a variable-length header extension area. The fixed fields are:

COPY moves data between PostgreSQL tables and standard file-system files. COPY TO copies the contents of a table to a file, while COPY FROM copies data from a file to a table (appending the data to whatever is in the table already). COPY TO can also copy the results of a SELECT query.

Forces quoting to be used for all non-NULL values in each specified column. NULL output is never quoted. If * is specified, non-NULL values will be quoted in all columns. This option is allowed only in COPY TO, and only when using CSV format.

The file trailer consists of a 16-bit integer word containing -1. This is easily distinguished from a tuple's field-count word.

Specifies whether the selected option should be turned on or off. You can write TRUE, ON, or 1 to enable the option, and FALSE, OFF, or 0 to disable it. The boolean value can also be omitted, in which case TRUE is assumed.

32-bit integer bit mask to denote important aspects of the file format. Bits are numbered from 0 (LSB) to 31 (MSB). Note that this field is stored in network byte order (most significant byte first), as are all the integer fields used in the file format. Bits 16–31 are reserved to denote critical file format issues; a reader should abort if it finds an unexpected bit set in this range. Bits 0–15 are reserved to signal backwards-compatible format issues; a reader should simply ignore any unexpected bits set in this range. Currently only one flag bit is defined, and the rest must be zero:

Specifies the character that separates columns within each row (line) of the file. The default is a tab character in text format, a comma in CSV format. This must be a single one-byte character. This option is not allowed when using binary format.

Specifies that the file contains a header line with the names of each column in the file. On output, the first line contains the column names from the table. On input, the first line is discarded when this option is set to true (or equivalent Boolean value). If this option is set to MATCH, the number and names of the columns in the header line must match the actual column names of the table, in order; otherwise an error is raised. This option is not allowed when using binary format. The MATCH option is only valid for COPY FROM commands.

The path name of the input or output file. An input file name can be an absolute or relative path, but an output file name must be an absolute path. Windows users might need to use an E'' string and double any backslashes used in the path name.

If OIDs are included in the file, the OID field immediately follows the field-count word. It is a normal field except that it's not included in the field-count. Note that oid system columns are not supported in current versions of PostgreSQL.

Kohärenz

Kohärentes Licht findet Anwendung in Laser-Chirurgie, Laser-Druckern, Laser-Scannern und in der Faser-Optik-Kommunikation.

Ein Laser ist ein Gerät, das kohärentes Licht erzeugt, indem es eine stimulierte Emission von Photonen aus einem angeregten Medium erzeugt, wodurch eine einheitliche Wellenfront mit gleichbleibender Phase entsteht.

Currently, subqueries are not allowed in WHERE expressions, and the evaluation does not see any changes made by the COPY itself (this matters when the expression contains calls to VOLATILE functions).

Many programs produce strange and occasionally perverse CSV files, so the file format is more a convention than a standard. Thus you might encounter some files that cannot be imported using this mechanism, and COPY might produce files that other programs cannot process.

For identity columns, the COPY FROM command will always write the column values provided in the input data, like the INSERT option OVERRIDING SYSTEM VALUE.

Kohärentes Licht hat Wellen, die in einem konstanten Phase-Verhältnis zueinander stehen, während bei inkohärentem Licht die Phasenbeziehungen zufällig sind und das Wellenmuster unregelmäßig ist.

CSV format will both recognize and produce CSV files with quoted values containing embedded carriage returns and line feeds. Thus the files are not strictly one line per table row like text-format files.

Kohärentes Licht beschreibt eine Lichtquelle, bei der die Lichtwellen in einer konstanten Phase zueinander stehen. Das bedeutet, die Phasenverschiebung zwischen den Wellen ändert sich nicht mit der Zeit.

Specifies how to behave when encountering an error converting a column's input value into its data type. An error_action value of stop means fail the command, while ignore means discard the input row and continue with the next one. The default is stop.

End of data can be represented by a single line containing just backslash-period (\.). An end-of-data marker is not necessary when reading from a file, since the end of file serves perfectly well; it is needed only when copying data to or from client applications using pre-3.0 client protocol.

A NOTICE message containing the ignored row count is emitted at the end of the COPY FROM if at least one row was discarded. When LOG_VERBOSITY option is set to verbose, a NOTICE message containing the line of the input file and the column name whose input conversion has failed is emitted for each discarded row.

It is strongly recommended that applications generating COPY data convert data newlines and carriage returns to the \n and \r sequences respectively. At present it is possible to represent a data carriage return by a backslash and carriage return, and to represent a data newline by a backslash and newline. However, these representations might not be accepted in future releases. They are also highly vulnerable to corruption if the COPY file is transferred across different machines (for example, from Unix to Windows or vice versa).

When the text format is used, the data read or written is a text file with one line per table row. Columns in a row are separated by the delimiter character. The column values themselves are strings generated by the output function, or acceptable to the input function, of each attribute's data type. The specified null string is used in place of columns that are null. COPY FROM will raise an error if any line of the input file contains more or fewer columns than are expected.

Specifies that the file is encoded in the encoding_name. If this option is omitted, the current client encoding is used. See the Notes below for more details.

Any other backslashed character that is not mentioned in the above table will be taken to represent itself. However, beware of adding backslashes unnecessarily, since that might accidentally produce a string matching the end-of-data marker (\.) or the null string (\N by default). These strings will be recognized before any other backslash processing is done.

KohärentBeispiel

Specifies the string that represents a null value. The default is \N (backslash-N) in text format, and an unquoted empty string in CSV format. You might prefer an empty string even in text format for cases where you don't want to distinguish nulls from empty strings. This option is not allowed when using binary format.

Specifies the character that should appear before a data character that matches the QUOTE value. The default is the same as the QUOTE value (so that the quoting character is doubled if it appears in the data). This must be a single one-byte character. This option is allowed only when using CSV format.

Requests copying the data with rows already frozen, just as they would be after running the VACUUM FREEZE command. This is intended as a performance option for initial data loading. Rows will be frozen only if the table being loaded has been created or truncated in the current subtransaction, there are no cursors open and there are no older snapshots held by this transaction. It is currently not possible to perform a COPY FREEZE on a partitioned table. This option is only allowed in COPY FROM.

If row-level security is enabled for the table, the relevant SELECT policies will apply to COPY table TO statements. Currently, COPY FROM is not supported for tables with row-level security. Use equivalent INSERT statements instead.

Note that the command is invoked by the shell, so if you need to pass any arguments that come from an untrusted source, you must be careful to strip or escape any special characters that might have a special meaning for the shell. For security reasons, it is best to use a fixed command string, or at least avoid including any user input in it.

Input data is interpreted according to ENCODING option or the current client encoding, and output data is encoded in ENCODING or the current client encoding, even if the data does not pass through the client but is read from or written to a file directly by the server.

KohärentSynonym

An optional list of columns to be copied. If no column list is specified, all columns of the table except generated columns will be copied.

The binary format option causes all data to be stored/read as binary format rather than as text. It is somewhat faster than the text and CSV formats, but a binary-format file is less portable across machine architectures and PostgreSQL versions. Also, the binary format is very data type specific; for example it will not work to output binary data from a smallint column and read it into an integer column, even though that would work fine in text format.

32-bit integer, length in bytes of remainder of header, not including self. Currently, this is zero, and the first tuple follows immediately. Future changes to the format might allow additional data to be present in the header. A reader should silently skip over any header extension data it does not know what to do with.

The values in each record are separated by the DELIMITER character. If the value contains the delimiter character, the QUOTE character, the NULL string, a carriage return, or line feed character, then the whole value is prefixed and suffixed by the QUOTE character, and any occurrence within the value of a QUOTE character or the ESCAPE character is preceded by the escape character. You can also use FORCE_QUOTE to force quotes when outputting non-NULL values in specific columns.

All backslash sequences are interpreted after encoding conversion. The bytes specified with the octal and hex-digit backslash sequences must form valid characters in the database encoding.

When using COPY FROM, any data item that matches this string will be stored as a null value, so you should make sure that you use the same string as you used with COPY TO.

The header extension area is envisioned to contain a sequence of self-identifying chunks. The flags field is not intended to tell readers what is in the extension area. Specific design of header extension contents is left for a later release.

Kohärentes Licht findet Anwendung in der Laseraugen-Chirurgie, bei der präzise Schnitte in der Netzhaut gemacht werden müssen.

It is recommended that the file name used in COPY always be specified as an absolute path. This is enforced by the server in the case of COPY TO, but for COPY FROM you do have the option of reading from a file specified by a relative path. The path will be interpreted relative to the working directory of the server process (normally the cluster's data directory), not the client's working directory.

Washeißtkohärentauf deutsch

This format option is used for importing and exporting the Comma Separated Value (CSV) file format used by many other programs, such as spreadsheets. Instead of the escaping rules used by PostgreSQL's standard text format, it produces and recognizes the common CSV escaping mechanism.

In CSV format, all characters are significant. A quoted value surrounded by white space, or any characters other than DELIMITER, will include those characters. This can cause errors if you import data from a system that pads CSV lines with white space out to some fixed width. If such a situation arises you might need to preprocess the CSV file to remove the trailing white space, before importing the data into PostgreSQL.

Do not match the specified columns' values against the null string. In the default case where the null string is empty, this means that empty values will be read as zero-length strings rather than nulls, even when they are not quoted. If * is specified, the option will be applied to all columns. This option is allowed only in COPY FROM, and only when using CSV format.

For INSERT, UPDATE, DELETE, and MERGE queries a RETURNING clause must be provided, and the target relation must not have a conditional rule, nor an ALSO rule, nor an INSTEAD rule that expands to multiple statements.

11-byte sequence PGCOPY\n\377\r\n\0 — note that the zero byte is a required part of the signature. (The signature is designed to allow easy identification of files that have been munged by a non-8-bit-clean transfer. This signature will be changed by end-of-line-translation filters, dropped zero bytes, dropped high bits, or parity changes.)

Backslash characters (\) can be used in the COPY data to quote data characters that might otherwise be taken as row or column delimiters. In particular, the following characters must be preceded by a backslash if they appear as part of a column value: backslash itself, newline, carriage return, and the current delimiter character.

If you see anything in the documentation that is not correct, does not match your experience with the particular feature or requires further clarification, please use this form to report a documentation issue.

Files named in a COPY command are read or written directly by the server, not by the client application. Therefore, they must reside on or be accessible to the database server machine, not the client. They must be accessible to and readable or writable by the PostgreSQL user (the user ID the server runs as), not the client. Similarly, the command specified with PROGRAM is executed directly by the server, not by the client application, must be executable by the PostgreSQL user. COPY naming a file or command is only allowed to database superusers or users who are granted one of the roles pg_read_server_files, pg_write_server_files, or pg_execute_server_program, since it allows reading or writing any file or running a program that the server has privileges to access.

Kohärentes Licht ist für die Datenübertragung effizienter, weil das Signal stärker und zentriert ist, es ermöglicht eine schnellere und klarere Übertragung von Informationen.

KohärentBedeutung

If 1, OIDs are included in the data; if 0, not. Oid system columns are not supported in PostgreSQL anymore, but the format still contains the indicator.

COPY with a file name instructs the PostgreSQL server to directly read from or write to a file. The file must be accessible by the PostgreSQL user (the user ID the server runs as) and the name must be specified from the viewpoint of the server. When PROGRAM is specified, the server executes the given command and reads from the standard output of the program, or writes to the standard input of the program. The command must be specified from the viewpoint of the server, and be executable by the PostgreSQL user. When STDIN or STDOUT is specified, data is transmitted via the connection between the client and the server.

Because backslash is not a special character in the CSV format, \., the end-of-data marker, could also appear as a data value. To avoid any misinterpretation, a \. data value appearing as a lone entry on a line is automatically quoted on output, and on input, if quoted, is not interpreted as the end-of-data marker. If you are loading a file created by another application that has a single unquoted column and might have a value of \., you might need to quote that value in the input file.

Note that all other sessions will immediately be able to see the data once it has been successfully loaded. This violates the normal rules of MVCC visibility and users should be aware of the potential problems this might cause.

If a column list is specified, COPY TO copies only the data in the specified columns to the file. For COPY FROM, each field in the file is inserted, in order, into the specified column. Table columns not specified in the COPY FROM column list will receive their default values.

The COPY FROM command physically inserts input rows into the table as it progresses. If the command fails, these rows are left in a deleted state; these rows will not be visible, but still occupy disk space. This might amount to considerable wasted disk space if the failure happened well into a large copy operation. VACUUM should be used to recover the wasted space.

COPY input and output is affected by DateStyle. To ensure portability to other PostgreSQL installations that might use non-default DateStyle settings, DateStyle should be set to ISO before using COPY TO. It is also a good idea to avoid dumping data with IntervalStyle set to sql_standard, because negative interval values might be misinterpreted by a server that has a different setting for IntervalStyle.

Kohärentes Licht ist die Voraussetzung, um Interferenz zu erzeugen (und alle damit verbundenen physikalischen “Phänomene”). Oft wird kohärentes Licht mit monochromatischem Licht gleichgesetzt, was nicht ganz korrekt ist. Kohärentes Licht ist eine elektromagnetische Welle mit nur einer bestimmten “Wellenlänge” (=> einfarbiges Licht). Im Gegensatz zu monochromatischem Lichtbesteht zwischen den einzelnen Wellen (zusätzlich) eine feste Phasenverschiebung.

By default, COPY will fail if it encounters an error during processing. For use cases where a best-effort attempt at loading the entire file is desired, the ON_ERROR clause can be used to specify some other behavior.

Specifies the string that represents a default value. Each time the string is found in the input file, the default value of the corresponding column will be used. This option is allowed only in COPY FROM, and only when not using binary format.

COPY TO will terminate each row with a Unix-style newline (“\n”). Servers running on Microsoft Windows instead output carriage return/newline (“\r\n”), but only for COPY to a server file; for consistency across platforms, COPY TO STDOUT always sends “\n” regardless of server platform. COPY FROM can handle lines ending with newlines, carriage returns, or carriage return/newlines. To reduce the risk of error due to un-backslashed newlines or carriage returns that were meant as data, COPY FROM will complain if the line endings in the input are not all alike.

Specifies the quoting character to be used when a data value is quoted. The default is double-quote. This must be a single one-byte character. This option is allowed only when using CSV format.

The CSV format has no standard way to distinguish a NULL value from an empty string. PostgreSQL's COPY handles this by quoting. A NULL is output as the NULL parameter string and is not quoted, while a non-NULL value matching the NULL parameter string is quoted. For example, with the default settings, a NULL is written as an unquoted empty string, while an empty string data value is written with double quotes (""). Reading values follows similar rules. You can use FORCE_NOT_NULL to prevent NULL input comparisons for specific columns. You can also use FORCE_NULL to convert quoted null string data values to NULL.

In der Kommunikation, besonders in der Faseroptik, ermöglicht kohärentes Licht die Übertragung von Daten über große Entfernungen ohne signifikanten Signalverlust.

You must have select privilege on the table whose values are read by COPY TO, and insert privilege on the table into which values are inserted by COPY FROM. It is sufficient to have column privileges on the column(s) listed in the command.

COPY TO can be used only with plain tables, not views, and does not copy rows from child tables or child partitions. For example, COPY table TO copies the same rows as SELECT * FROM ONLY table. The syntax COPY (SELECT * FROM table) TO ... can be used to dump all of the rows in an inheritance hierarchy, partitioned table, or view.

where condition is any expression that evaluates to a result of type boolean. Any row that does not satisfy this condition will not be inserted to the table. A row satisfies the condition if it returns true when the actual row values are substituted for any variable references.