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# CXI. PostgreSQL 数据库函数

# 简介

PostgreSQL 是一个开放源码的免费数据库系统。Postgres 最初由加州大学伯克利分校计算机科学系开发，倡导了很多关系对象的观念，这些观念现在已经用在一些商业数据库系统中。它提供了 SQL92/SQL99 语言支持，事务处理，引用集成，存储过程以及类型扩展。PostgreSQL 则是 Postgres 的一个开放源代码的后代。

# 需求

要使用 PostgreSQL 支持，需要 PostgreSQL 6.5 或更新版本，PostgreSQL 8.0 或更新版本来使用所有的 PostgreSQL 模块。PostgreSQL 支持多种字符编码包括多字节字符编码。关于 PostgreSQL 的当前版本以及更多信息见 http://www.postgresql.org/ 以及 PostgreSQL 文档。

# 安装

为添加 PostgreSQL 支持，在编译 PHP 时需要加上 --with-pgsql[=DIR] 选项。如果可以用共享模块方式，PostgreSQL 模块可以在 `php.ini` 用 extension 指令或者 dl() 函数加载。

# 运行时配置

这些函数的行为受 `php.ini` 的影响。

表格 1. PostgreSQL 配置选项

名称 | 默认值 | 可变范围 | 更新日志
--- | --- | --- | ---
pgsql.allow_persistent | "1" | PHP_INI_SYSTEM |
pgsql.max_persistent | "-1" | PHP_INI_SYSTEM |
pgsql.max_links | "-1" | PHP_INI_SYSTEM |
pgsql.auto_reset_persistent | "0" | PHP_INI_SYSTEM | 从 PHP 4.2.0 起开始存在
pgsql.ignore_notice | "0" | PHP_INI_ALL | 从 PHP 4.3.0 起开始存在
pgsql.log_notice | "0" | PHP_INI_ALL | 从 PHP 4.3.0 起开始存在

有关 PHP_INI_* 常量进一步的细节与定义参见附录 G。

以下是配置选项的简要解释。

pgsql.allow_persistent boolean

  是否允许持久的 Postgres 连接。

pgsql.max_persistent integer

  每个进程所能有的持久 Postgres 连接数目。

pgsql.max_links integer

  每个进程所能有的 Postgres 连接数目，包括持久连接。

pgsql.auto_reset_persistent integer

  检测用在 pg_pconnect() 上的中断了的持久连接。需要一些损耗。

pgsql.ignore_notice integer

  是否忽略 PostgreSQL 后端的通告。

pgsql.log_notice integer

  是否记录 PostgreSQL 后端的通告消息。要记录通告消息日志，PHP 指令 pgsql.ignore_notice 必须为 off。

# 资源类型

PostgreSQL 模块使用了两种资源类型。第一种是数据库连接的标识符，第二种是保存查询结果的资源。

# 预定义常量

以下常量由本扩展模块定义，因此只有在本扩展模块被编译到 PHP 中，或者在运行时被动态加载后才有效。

`PGSQL_ASSOC` (integer)

  Passed to pg_fetch_array(). Return an associative array of field names and values.

`PGSQL_NUM` (integer)

  Passed to pg_fetch_array(). Return a numerically indexed array of field numbers and values.

`PGSQL_BOTH` (integer)

  Passed to pg_fetch_array(). Return an array of field values that is both numerically indexed (by field number) and associated (by field name).

`PGSQL_CONNECT_FORCE_NEW` (integer)

  Passed to pg_connect() to force the creation of a new connection, rather then re-using an existing identical connection.

`PGSQL_CONNECTION_BAD` (integer)

  Returned by pg_connection_status() indicating that the database connection is in an invalid state.

`PGSQL_CONNECTION_OK` (integer)

  Returned by pg_connection_status() indicating that the database connection is in a valid state.

`PGSQL_SEEK_SET` (integer)

  Passed to pg_lo_seek(). Seek operation is to begin from the start of the object.

`PGSQL_SEEK_CUR` (integer)

  Passed to pg_lo_seek(). Seek operation is to begin from the current position.

`PGSQL_SEEK_END` (integer)

  Passed to pg_lo_seek(). Seek operation is to begin from the end of the object.

`PGSQL_EMPTY_QUERY` (integer)

  Returned by pg_result_status(). The string sent to the server was empty.

`PGSQL_COMMAND_OK` (integer)

  Returned by pg_result_status(). Successful completion of a command returning no data.

`PGSQL_TUPLES_OK` (integer)

  Returned by pg_result_status(). Successful completion of a command returning data (such as a SELECT or SHOW).

`PGSQL_COPY_OUT` (integer)

  Returned by pg_result_status(). Copy Out (from server) data transfer started.

`PGSQL_COPY_IN` (integer)

  Returned by pg_result_status(). Copy In (to server) data transfer started.

`PGSQL_BAD_RESPONSE` (integer)

  Returned by pg_result_status(). The server's response was not understood.

`PGSQL_NONFATAL_ERROR` (integer)

  Returned by pg_result_status(). A nonfatal error (a notice or warning) occurred.

`PGSQL_FATAL_ERROR` (integer)

  Returned by pg_result_status(). A fatal error occurred.

`PGSQL_TRANSACTION_IDLE` (integer)

  Returned by pg_transaction_status(). Connection is currently idle, not in a transaction.

`PGSQL_TRANSACTION_ACTIVE` (integer)

  Returned by pg_transaction_status(). A command is in progress on the connection. A query has been sent via the connection and not yet completed.

`PGSQL_TRANSACTION_INTRANS` (integer)

  Returned by pg_transaction_status(). The connection is idle, in a transaction block.

`PGSQL_TRANSACTION_INERROR` (integer)

  Returned by pg_transaction_status(). The connection is idle, in a failed transaction block.

`PGSQL_TRANSACTION_UNKNOWN` (integer)

  Returned by pg_transaction_status(). The connection is bad.

`PGSQL_DIAG_SEVERITY` (integer)

  Passed to pg_result_error_field(). The severity; the field contents are ERROR, FATAL, or PANIC (in an error message), or WARNING, NOTICE, DEBUG, INFO, or LOG (in a notice message), or a localized translation of one of these. Always present.

`PGSQL_DIAG_SQLSTATE` (integer)

  Passed to pg_result_error_field(). The SQLSTATE code for the error. The SQLSTATE code identifies the type of error that has occurred; it can be used by front-end applications to perform specific operations (such as error handling) in response to a particular database error. This field is not localizable, and is always present.

`PGSQL_DIAG_MESSAGE_PRIMARY` (integer)

  Passed to pg_result_error_field(). The primary human-readable error message (typically one line). Always present.

`PGSQL_DIAG_MESSAGE_DETAIL` (integer)

  Passed to pg_result_error_field(). Detail: an optional secondary error message carrying more detail about the problem. May run to multiple lines.

`PGSQL_DIAG_MESSAGE_HINT` (integer)

  Passed to pg_result_error_field(). Hint: an optional suggestion what to do about the problem. This is intended to differ from detail in that it offers advice (potentially inappropriate) rather than hard facts. May run to multiple lines.

`PGSQL_DIAG_STATEMENT_POSITION` (integer)

  Passed to pg_result_error_field(). A string containing a decimal integer indicating an error cursor position as an index into the original statement string. The first character has index 1, and positions are measured in characters not bytes.

`PGSQL_DIAG_INTERNAL_POSITION` (integer)

  Passed to pg_result_error_field(). This is defined the same as the `PG_DIAG_STATEMENT_POSITION` field, but it is used when the cursor position refers to an internally generated command rather than the one submitted by the client. The `PG_DIAG_INTERNAL_QUERY` field will always appear when this field appears.

`PGSQL_DIAG_INTERNAL_QUERY` (integer)

  Passed to pg_result_error_field(). The text of a failed internally-generated command. This could be, for example, a SQL query issued by a PL/pgSQL function.

`PGSQL_DIAG_CONTEXT` (integer)

  Passed to pg_result_error_field(). An indication of the context in which the error occurred. Presently this includes a call stack traceback of active procedural language functions and internally-generated queries. The trace is one entry per line, most recent first.

`PGSQL_DIAG_SOURCE_FILE` (integer)

  Passed to pg_result_error_field(). The file name of the PostgreSQL source-code location where the error was reported.

`PGSQL_DIAG_SOURCE_LINE` (integer)

  Passed to pg_result_error_field(). The line number of the PostgreSQL source-code location where the error was reported.

`PGSQL_DIAG_SOURCE_FUNCTION` (integer)

  Passed to pg_result_error_field(). The name of the PostgreSQL source-code function reporting the error.

`PGSQL_ERRORS_TERSE` (integer)

  Passed to pg_set_error_verbosity(). Specified that returned messages include severity, primary text, and position only; this will normally fit on a single line.

`PGSQL_ERRORS_DEFAULT` (integer)

  Passed to pg_set_error_verbosity(). The default mode produces messages that include the above plus any detail, hint, or context fields (these may span multiple lines).

`PGSQL_ERRORS_VERBOSE` (integer)

  Passed to pg_set_error_verbosity(). The verbose mode includes all available fields.

`PGSQL_STATUS_LONG` (integer)

  Passed to pg_result_status(). Indicates that numerical result code is desired.

`PGSQL_STATUS_STRING` (integer)

  Passed to pg_result_status(). Indicates that textual result command tag is desired.

`PGSQL_CONV_IGNORE_DEFAULT` (integer)

  Passed to pg_convert(). Ignore default values in the table during conversion.

`PGSQL_CONV_FORCE_NULL` (integer)

  Passed to pg_convert(). Use SQL NULL in place of an empty string.

`PGSQL_CONV_IGNORE_DEFAULT` (integer)

  Passed to pg_convert(). Ignore conversion of `NULL` into SQL NOT NULL columns.

# 注释

> 注: 不是所有的版本都支持所有的函数，这和 libpq（PostgreSQL C 客户端库）的版本和编译方法有关。如果 PHP 的 PostgreSQL 扩展不见了，那是因为 libpq 的版本不支持它。

> 注: 大多数 PostgreSQL 函数接受 connection 作为第一个可选参数。如果没有提供，则使用上一个打开的连接。如果没有打开的连接，函数返回 `FALSE`。

> 注: PostgreSQL 在创建对象和查询时自动将所有标识符（例如表／列名）转成小写字母值。要强制其使用混合或大写字母的标识符，必须将标识符用双引号（"）转义。

> 注: PostgreSQL 没有特殊的命令来取得数据库的结构信息（例如当前数据库中的所有表）。不过在 PostgreSQL 7.4 及以上版本有一个标准结构名叫 information_schema，它包含有系统视图以及所有必要的信息，可以很容易地查询出来。其细节见 PostgreSQL 文档。

# 范例

此简单例子演示了 PostgreSQL 数据库的连接，执行查询，显示结果以及断开连接。

例子 1. PostgreSQL 例子

`<?php
// 连接，选择数据库
$db = pg_connect("host=localhost dbname=publishing user=www password=foo");
or die('Could not connect: ' . pg_last_error());
// 执行 SQL 查询
$query = 'SELECT * FROM authors';
$result = pg_query($query) or die('Query failed: ' . pg_last_error());
// 用 HTML 显示结果
echo "<table>\n";
while ($line = pg_fetch_array($result, null, PGSQL_ASSOC)) {
echo "\t<tr>\n";
foreach ($line as $col_value) {
echo "\t\t<td>$col_value</td>\n";
}
echo "\t</tr>\n";
}
echo "</table>\n";
// 释放结果集
pg_free_result($result);
// 关闭连接
pg_close($link);
?>`

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