PostgreSQL Processing With gawk

Table of Contents

General Introduction

This file documents the PostgreSQL extension of GNU Awk (gawk) version 4.1.1 and later.

Copyright (C) 2000–2002, 2004–2007, 2014 Free Software Foundation, Inc.

This is Edition 1.0 of PostgreSQL Processing With gawk, for the 1.0.2 (or later) version of the PostgreSQL extension of the GNU implementation of AWK.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with the Invariant Sections being “GNU General Public License”, with the Front-Cover Texts being “A GNU Manual”, and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled “GNU Free Documentation License”.

1. The FSF’s Back-Cover Text is: “You have the freedom to copy and modify this GNU manual.”

1 PostgreSQL API Reference

The functions described here are intended to expose the libpq C API as documented at //http://www.postgresql.org/docs/8.0/interactive/libpq.html. This documentation can be understood only in conjunction with the libpq documentation.

This API can be used by either invoking gawk with a command-line argument of -l pgsql or by inserting @load "pgsql" in your script.

Optional parameters are enclosed in square brackets ([ ]).

1.1 Database Connection Control Functions

pg_connect([conninfo])

Initiate a database connection. The argument string conninfo is passed to the PQconnectdb function. On success, a unique, opaque connection handle is returned. On failure, a null string ("") is returned, and ERRNO is set.

pg_connectdb([conninfo])

This function is simply an alias for pg_connect.

pg_disconnect(conn)

Call the PQfinish function with the handle indicated by conn. The conn handle must have been returned by a previous call to pg_connect. If the handle is not found, then -1 is returned and ERRNO is set. On success, 0 is returned and the connection associated with conn is no longer active.

pg_finish(conn)

This function is simply an alias for pg_disconnect.

pg_reset(conn)

Call the PQreset function with the handle indicated by conn. The conn handle must have been returned by a previous call to pg_connect. If the handle is not found, then -1 is returned and ERRNO is set. Otherwise, PQreset is called. If the subsequent value returned by PQstatus is CONNECTION_OK, then 0 is returned, otherwise -1 is returned and ERRNO is set.

pg_reconnect(conn)

This function is simply an alias for pg_reset.

1.2 Connection Status Functions

pg_serverversion(conn)

This function calls PQserverVersion on the specified connection and returns the integer value. If the connection is not found, the return value is zero, and ERRNO is set.

pg_errormessage(conn)

This function calls PQerrorMessage on the specified connection and returns the result. If the connection is not found, the return value is a null string (""), and ERRNO is set.

1.3 Control Functions

pg_clientencoding(conn)

This function calls PQclientEncoding on the specified connection, and then returns the result of calling pg_encoding_to_char on the value returned. If the connection is not found or an error occurs, the return value is a null string (""), and ERRNO is set.

pg_setclientencoding(conn, encoding)

This function calls PQsetClientEncoding for the specified connection and encoding. If an error occurs, it sets ERRNO and returns -1. Otherwise, it returns the value from PQsetClientEncoding, which should be zero on success.

1.4 Command Execution Functions

pg_getresult(conn)

If the connection is not found, a null string ("") is returned, and ERRNO is set. Otherwise, PQgetResult is called on the given connection. If it returns NULL, then it returns a NULL string (""). If the PGresult returned is non-NULL, then the return value depends on the value of PQresultStatus(PQgetResult(conn)) as follows:

PGRES_TUPLES_OK

The function returns an string handle that can be used to access the rows returned by the SQL query. The format of the string handle is: TUPLES <# of rows> <unique identifier>. You can find the number of rows being returned by extracting the 2nd word of the returned handle, or by calling the pg_ntuples function. The returned string handle is mapped to a PGresult pointer for use in subsequently extracting the returned data.

PGRES_COMMAND_OK

First, we call PQcmdTuples and then we return a string in this format: OK <result of PQcmdTuples>. Since there is no data being returned, we call PQclear automatically.

PGRES_EMPTY_QUERY

This is handled the same way as PGRES_COMMAND_OK.

PGRES_COPY_IN

The returned string has this format: COPY_IN <PQnfields(res)> {BINARY|TEXT}. Since there is no data being returned, we call PQclear automatically. The user code may subsequently call pg_putcopydata to transmit bulk data to the server (and use pg_putcopyend to terminate the transfer).

PGRES_COPY_OUT

The returned string has this format: COPY_OUT <PQnfields(res)> {BINARY|TEXT}. Since there is no data being returned, we call PQclear automatically. The user code should subsequently call pg_getcopydata until it returns a NULL string ("").

default (unhandled value)

This is an unhandled return value, so we return a standardized error string in this format: ERROR [BADCONN ]<status> where BADCONN is included if PQstatus(conn) does not equal CONNECTION_OK, and the subsequent string is the result of calling PQresStatus(PQresultStatus(res)). And we set ERRNO to the string returned by PQresultErrorMessage(res). Since there is no data being returned, we call PQclear automatically.

pg_clear(res)

If the result handle is not found, -1 is returned, and ERRNO is set. Otherwise, PQclear(res) is called and 0 is returned.

pg_exec(conn, command)

If the connection is not found, a null string ("") is returned, and ERRNO is set. Otherwise, PQexec is called with the command string. If PQexec returns NULL, then the returned value will start with the "ERROR ". If PQstatus does not return CONNECTION_OK, then the next word in the returned value will be "BADCONN". Then the result of calling PQresStatus(PQresultStatus(NULL)) will be appended to the string. In addition, ERRNO will be set to the string returned by PQerrorMessage. On the other hand, if PQexec does not return NULL, then the result will be in the standard format returned by pg_getresult.

pg_execparams(conn, command, nParams [, paramValues])

If the connection is not found, or nParams is negative, a null string ("") is returned, and ERRNO is set. Otherwise, PQexecParams is called with the paramTypes, paramLengths, and paramFormats arguments set to NULL. The paramValues array is used by searching for the value corresponding to $n in paramValues[n]. The return value is the same as for pg_exec.

pg_prepare(conn, command)

If the connection is not found, a null string ("") is returned, and ERRNO is set. Otherwise, PQprepare is called with the command string. If PQprepare returns NULL, or if PQresultStatus(result) != PGRES_COMMAND_OK, then the function returns a NULL string "" and sets ERRNO. Otherwise, if successful, an opaque statement handle is returned that can be used with pg_execprepared or pg_sendqueryprepared.

pg_execprepared(conn, stmtName, nParams [, paramValues])

This function behaves the same way as pg_execparams, except that it requires a prepared statement handle as the second argument instead of an SQL command.

1.5 Asynchronous Command Processing

pg_sendquery(conn, command)

If the connection is not found, 0 is returned, and ERRNO is set. Otherwise, PQsendQuery is called with the given command, and the result is returned (should be 0 for failure and 1 for success). If the return code is 0, then ERRNO will be set. You should call pg_getresult to retrieve the results. You must call pg_getresult until it returns a NULL string ("").

pg_sendqueryparams(conn, command, nParams [, paramValues])

If the connection is not found, or nParams is negative, then 0 is returned, and ERRNO is set. Otherwise, PQsendQueryParams is called with the paramTypes, paramLengths, and paramFormats arguments set to NULL, and the result is returned. As in pg_execparams, the value corresponding to $n should be in paramValues[n]. If the return code is 0, ERRNO will be set.

pg_sendprepare(conn, command)

If the connection is not found, a null string ("") is returned, and ERRNO is set. Otherwise, PQsendPrepare is called with the command string. If PQsendPrepare returns 0, then the function returns a NULL string "" and sets ERRNO. Otherwise, an opaque statement handle is returned that can be used with pg_sendqueryprepared or pg_execprepared. You should call pg_getresult to ascertain whether the command completed successfully.

pg_sendqueryprepared(conn, stmtName, nParams [, paramValues])

This function behaves the same way as pg_sendqueryparams, except that it requires a prepared statement handle as the second argument instead of an SQL command.

1.6 Functions for Sending and Receiving COPY Data

pg_putcopydata(conn, buffer)

If the connection is not found, -1 is returned, and ERRNO is set. Otherwise, PQputCopyData is called with the buffer argument, and its value is returned. If PQputCopyData returns -1, then ERRNO is set.

pg_putcopyend(conn [, errormsg])

If the connection is not found, -1 is returned, and ERRNO is set. Otherwise, PQputCopyEnd is called with the optional errormsg argument if supplied, and its value is returned. If PQputCopyEnd returns -1, then ERRNO is set.

pg_getcopydata(conn)

If the connection is not found, a NULL string ("") is returned, and ERRNO is set. Otherwise, PQgetCopyData is called with the async argument set to FALSE. If PQgetCopyData returns -1, then the copy is done, and a NULL string ("") is returned (and the user should call pg_getresult to obtain the final result status of the COPY command). If the return code is -2 indicating an error, then a NULL string ("") is returned, and ERRNO is set. Otherwise, the retrieved row is returned.

Please note that starting with version 2 of the API available in gawk 4.2, a successfully retrieved row will be flagged as user input data eligible for the strnum attribute. So if the value appears to be numeric, gawk will treat it as a number in comparisons. This feature was not available prior to version 2 of the gawk API.

1.7 Retrieving Query Result Information

pg_nfields(res)

If the res argument result handle is not found, -1 is returned and ERRNO is set. Otherwise, the value of PQnfields(res) is returned.

pg_ntuples(res)

If the res argument result handle is not found, -1 is returned and ERRNO is set. Otherwise, the value of PQntuples(res) is returned.

pg_fname(res, column_number)

If the res argument result handle is not found, or if column_number is out of range, a NULL string ("") is returned and ERRNO is set. Otherwise, the value of PQfname(res, column_number) is returned.

pg_getvalue(res, row_number, column_number)

If the res argument result handle is not found, or if row_number or column_number is out of range, a NULL string ("") is returned and ERRNO is set. Otherwise, the value of PQgetvalue(res, row_number, column_number) is returned.

Please note that starting with version 2 of the API available in gawk 4.2, the result will be flagged as user input data eligible for the strnum attribute. So if the value appears to be numeric, gawk will treat it as a number in comparisons. This feature was not available prior to version 2 of the gawk API.

pg_getisnull(res, row_number, column_number)

If the res argument result handle is not found, or if row_number or column_number is out of range, -1 is returned and ERRNO is set. Otherwise, the value of PQgetisnull(res, row_number, column_number) is returned (1 if the data is NULL, and 0 if it is non-NULL).

1.8 Higher-level Functions to Retrieve Query Results Using Arrays

pg_fields(res, field_names)

If the res argument result handle is not found, -1 is returned and ERRNO is set. Otherwise, the number of fields in the result (i.e. pg_nfields(res)) is returned, and the array field_names is cleared and populated with the column names as follows: field_names[col] contains the value returned by PQfname(res, col).

pg_fieldsbyname(res, field_names)

If the res argument result handle is not found, -1 is returned and ERRNO is set. Otherwise, the number of fields in the result (i.e. pg_nfields(res)) is returned, and the array field_names is cleared and populated with the column names as follows: field_names[PQfname(res, col)] contains col.

pg_getrow(res, row_number, field)

If the res argument result handle is not found, or if row_number is out of range, then -1 is returned and ERRNO is set. Otherwise, the number of non-NULL fields in the row is returned, and the field array is cleared and populated as follows: field[col_number] contains PQgetvalue(res, row_number, col_number) for all non-NULL columns.

Please note that starting with version 2 of the API available in gawk 4.2, the array values will be flagged as user input data eligible for the strnum attribute. So if the values appear to be numeric, gawk will treat them as numbers in comparisons. This feature was not available prior to version 2 of the gawk API.

pg_getrowbyname(res, row_number, field)

If the res argument result handle is not found, or if row_number is out of range, then -1 is returned and ERRNO is set. Otherwise, the number of non-NULL fields in the row is returned, and the field array is cleared and populated as follows: field[PQfname(res, col_number)] contains PQgetvalue(res, row_number, col_number) for all non-NULL columns.

Please note that starting with version 2 of the API available in gawk 4.2, the array values will be flagged as user input data eligible for the strnum attribute. So if the values appear to be numeric, gawk will treat them as numbers in comparisons. This feature was not available prior to version 2 of the gawk API.

Appendix A GNU Free Documentation License

Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
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10. FUTURE REVISIONS OF THIS LICENSE

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    “Incorporate” means to publish or republish a Document, in whole or in part, as part of another Document.

    An MMC is “eligible for relicensing” if it is licensed under this License, and if all works that were first published under this License somewhere other than this MMC, and subsequently incorporated in whole or in part into the MMC, (1) had no cover texts or invariant sections, and (2) were thus incorporated prior to November 1, 2008.

    The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on the same site at any time before August 1, 2009, provided the MMC is eligible for relicensing.

ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

  Copyright (C)  year  your name.
  Permission is granted to copy, distribute and/or modify this document
  under the terms of the GNU Free Documentation License, Version 1.3
  or any later version published by the Free Software Foundation;
  with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
  Texts.  A copy of the license is included in the section entitled ``GNU
  Free Documentation License''.

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with…Texts.” line with this:

    with the Invariant Sections being list their titles, with
    the Front-Cover Texts being list, and with the Back-Cover Texts
    being list.

If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.

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