</para>

<para>

To begin, call conn=PQconnectStart("&lt;connection_info_string&gt;"). If

conn is NULL, then libpq has been unable to allocate a new PGconn

To begin, call<literal>conn=PQconnectStart("&lt;connection_info_string&gt;")</literal>.

Ifconn is NULL, then libpq has been unable to allocate a new PGconn

structure. Otherwise, a valid PGconn pointer is returned (though not yet

representing a valid connection to the database). On return from

PQconnectStart, call status=PQstatus(conn). If status equals

<synopsis>

Oid PQoidValue(const PGresult *res);

</synopsis>

The type <type>Oid</type> and the constant <literal>Invalid</literal>

will be defined if you include the <application>libpq</application>

header file. They will both be some integer type.

</para>

</listitem>

<synopsis>

const char * PQoidStatus(const PGresult *res);

</synopsis>

The function is deprecated in favor of <function>PQoidValue</function>.

The function is deprecated in favor of <function>PQoidValue</function>

and is not thread-safe.

</para>

</listitem>

const PGresult *res,

const PQprintOpt *po);

struct_PQprintOpt{

pqbool header; /* print output field headings and row count */

pqbool align; /* fill align the fields */

pqbool standard; /* old brain dead format */

pqbool html3; /* output html tables */

pqbool expanded; /* expand tables */

pqbool pager; /* use pager for output if needed */

struct {

int header; /* print output field headings and row count */

int align; /* fill align the fields */

int standard; /* old brain dead format */

int html3; /* output html tables */

int expanded; /* expand tables */

int pager; /* use pager for output if needed */

char *fieldSep; /* field separator */

char *tableOpt; /* insert to HTML &lt;table ...&gt; */

char *caption; /* HTML &lt;caption&gt; */

char **fieldName; /* null terminated array of replacement field names */

}

} PQprintOpt;

</synopsis>

This functionis intended to replace PQprintTuples(), which is

<function>PQprint()</function> to display query results.

This functionwas formerly used by <application>psql</application>

function is no longer supported.

</para>

</listitem>

<listitem>

<para>

<function>PQprintTuples</function>

Prints out all the tuples and, optionally, the

attribute names to the specified output stream.

<synopsis>

void PQprintTuples(const PGresult *res,

FILE *fout, /* output stream */

int printAttName,/* print attribute names or not*/

int terseOutput, /* delimiter bars or not?*/

int width); /* width of column, variable width if 0*/

</synopsis>

</para>

</listitem>

<listitem>

<para>

<function>PQdisplayTuples</function>

Prints out all the tuples and, optionally, the

attribute names to the specified output stream.

<synopsis>

void PQdisplayTuples(const PGresult* res,

FILE *fout, /* output stream */

int fillAlign, /* space fill to align columns */

const char *fieldSep, /* field separator */

int printHeader, /* display headers? */

int quiet); /* suppress print of row count at end */

</synopsis>

<function>PQdisplayTuples()</function> was intended to supersede

<function>PQprintTuples()</function>, and

is in turn superseded by <function>PQprint()</function>.

</para>

</listitem>

<listitem>

<para>

<!--

$Header: /cvsroot/pgsql/doc/src/sgml/ref/abort.sgml,v 1.4 1999/07/22 15:09:05 thomas Exp $

$Header: /cvsroot/pgsql/doc/src/sgml/ref/abort.sgml,v 1.5 2000/01/29 16:58:27 petere Exp $

Postgres documentation

-->

<variablelist>

<varlistentry>

<term><computeroutput>

</computeroutput></term>

<listitem>

<para>

</varlistentry>

<varlistentry>

<term><computeroutput>

NOTICE:UserAbortTransactionBlock and not inin-progress state

NOTICE:ROLLBACK: no transaction in progress

</computeroutput></term>

<listitem>

<para>

SQL92

</title>

<para>

This command is a <productname>Postgres</productname> extension present

This command is a <productname>PostgreSQL</productname> extension present

for historical reasons. <command>ROLLBACK</command> is the <acronym>SQL92</acronym>

equivalent command.

</para>

<!--

$Header: /cvsroot/pgsql/doc/src/sgml/ref/alter_table.sgml,v 1.9 2000/01/09 17:35:27momjian Exp $

$Header: /cvsroot/pgsql/doc/src/sgml/ref/alter_table.sgml,v 1.10 2000/01/29 16:58:27petere Exp $

Postgres documentation

-->

<date>1999-07-20</date>

</refsynopsisdivinfo>

<synopsis>

ALTER TABLE <replaceable class="PARAMETER">table</replaceable>

[ * ]ADD [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> <replaceable

ALTER TABLE <replaceable class="PARAMETER">table</replaceable> [ * ]

ADD [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> <replaceable

class="PARAMETER">type</replaceable>

ALTER TABLE <replaceable class="PARAMETER">table</replaceable>

[ * ] RENAME [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> TO <replaceable

ALTER TABLE <replaceable class="PARAMETER">table</replaceable> [ * ]

ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> { SET DEFAULT <replaceable

class="PARAMETER">value</replaceable> | DROP DEFAULT }

ALTER TABLE <replaceable class="PARAMETER">table</replaceable> [ * ]

RENAME [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> TO <replaceable

class="PARAMETER">newcolumn</replaceable>

ALTER TABLE <replaceable class="PARAMETER">table</replaceable>

RENAME TO <replaceable class="PARAMETER">newtable</replaceable>

<term><replaceable class="PARAMETER"> newtable </replaceable></term>

<listitem>

<para>

New name foran existing column.

New name forthe table.

</para>

</listitem>

</varlistentry>

<variablelist>

<varlistentry>

<term><computeroutput>

ALTER

</computeroutput></term>

<term><computeroutput>ALTER</computeroutput></term>

<listitem>

<para>

Message returned from column or table renaming.

</varlistentry>

<varlistentry>

<term><computeroutput>

NEW

</computeroutput></term>

<listitem>

<para>

Message returned from column addition.

</para>

</listitem>

</varlistentry>

<varlistentry>

<term><computeroutput>

ERROR

</computeroutput></term>

<term><computeroutput>ERROR</computeroutput></term>

<listitem>

<para>

Message returned if table or column is not available.

</title>

<para>

<command>ALTER TABLE</command> changes the definition of an existing table.

The new columns and their types are specified in the same style

and with the the same restrictions as in <command>CREATE TABLE</command>.

The RENAME clause causes the name of a table or column

The <literal>ADD COLUMN</literal> form adds a new column to the table

using the same syntax as <xref linkend="SQL-CREATETABLE"

endterm="SQL-CREATETABLE-title">. The <literal>ALTER COLUMN</literal> form

allows you to set or remove the default for the column. Note that defaults

only apply to newly inserted rows.

The <literal>RENAME</literal> clause causes the name of a table or column

to change without changing any of the data contained in

the affected table. Thus, the table or column will

remain of the same type and size after this command is

</para>

<para>

For efficiency reasons, default values for added attributes are

not placed in existing instances of a class.

That is, existing instances will have NULL values in the new

attributes. If non-NULL values are desired, a subsequent

<command>UPDATE</command> query

(<xref linkend="sql-update-title" endterm="sql-update-title">)

should be run.

In the current implementation, default and constraint clauses for the

new column will be ignored. You can use the <literal>SET DEFAULT</literal>

form of <command>ALTER TABLE</command> to set the default later.

(You will also have to update the already existing rows to the

new default value, using <xref linkend="sql-update-title"

endterm="sql-update-title">.)

</para>

<para>

<refsect2info>

<date>1998-04-15</date>

</refsect2info>

<title>

SQL92

</title>

<para>

<command>ALTER TABLE/RENAME</command>

is a <productname>Postgres</productname> language extension.

</para>

<title>SQL92</title>

<para>

The <literal>ADD COLUMN</literal> form is compliant with the exception that

it does not support defaults and constraints, as explained above.

The <literal>ALTER COLUMN</literal> form is in full compliance.

</para>

<para>

SQL92 specifies some additional capabilities for <command>ALTER TABLE</command>

statement which are not yet directly supported by

<productname>Postgres</productname>:

</para>

<variablelist>

<varlistentry>

<term>

<synopsis>

ALTER TABLE <replaceable class="PARAMETER">table</replaceable> ALTER [

COLUMN ] <replaceable class="PARAMETER">column</replaceable>

SET DEFAULT <replaceable class="PARAMETER">default</replaceable>

ALTER TABLE <replaceable class="PARAMETER">table</replaceable> ALTER [

COLUMN ] <replaceable class="PARAMETER">column</replaceable>

ADD [ CONSTRAINT <replaceable class="PARAMETER">>constrain</replaceable>> ] <replaceable

class="PARAMETER">table-constraint</replaceable>

</synopsis>

</term>

<listitem>

<para>

Puts the default value or constraint specified into the

definition of column in the table.

See <command>CREATE TABLE</command> for the

syntax of the default and table-constraint clauses.

If a default clause already exists, it will be replaced by

the new definition. If any constraints on this column already

exist, they will be retained using a boolean AND with the new

constraint.

</para>

<para>

Currently, to set new default constraints on an existing column

the table must be recreated and reloaded:

<programlisting>

CREATE TABLE temp AS SELECT * FROM distributors;

DROP TABLE distributors;

CREATE TABLE distributors (

did DECIMAL(3) DEFAULT 1,

name VARCHAR(40) NOT NULL,

city VARCHAR(30)

);

INSERT INTO distributors SELECT * FROM temp;

DROP TABLE temp;

</programlisting>

</para>

</listitem>

</varlistentry>

<para>

SQL92 specifies some additional capabilities for <command>ALTER TABLE</command>

statement which are not yet directly supported by <productname>PostgreSQL</productname>:

<varlistentry>

<term>

<synopsis>

ALTER TABLE <replaceable class="PARAMETER">table</replaceable>

DROP DEFAULT <replaceable class="PARAMETER">default</replaceable>

ALTER TABLE <replaceable class="PARAMETER">table</replaceable>

DROP CONSTRAINT <replaceable class="PARAMETER">constraint</replaceable> { RESTRICT | CASCADE }

<variablelist>

<varlistentry>

<term>

<synopsis>

ALTER TABLE <replaceable class="PARAMETER">table</replaceable> ADD <replaceable class="PARAMETER">table constraint definition</replaceable>

ALTER TABLE <replaceable class="PARAMETER">table</replaceable> DROP CONSTRAINT <replaceable class="PARAMETER">constraint</replaceable> { RESTRICT | CASCADE }

</synopsis>

</term>

<listitem>

<para>

Removes the default value specified by default or the rule

specified by constraint from the definition of a table.

If RESTRICT is specified only a constraint with no dependent

constraints can be destroyed.

If CASCADE is specified, Any constraints that are dependent on

this constraint are also dropped.

Adds or removes a table constraint (such as a check constraint,

unique constraint, or foreign key constraint). To create

or remove a unique constraint, create or drop a unique index,

respectively (see <xref linkend="SQL-CREATEINDEX" endterm="SQL-CREATEINDEX-title">).

To change other kinds of constraints you need to recreate

and reload the table, using other parameters to the

<xref linkend="SQL-CREATETABLE" endterm="SQL-CREATETABLE-title">

command.

</para>

<para>

Currently, to remove a default value or constraints on an

existing column the table must be recreated and reloaded:

For example, to drop any constraints on a table <literal>distributors</literal>:

<programlisting>

CREATE TABLE temp AS SELECT * FROM distributors;

DROP TABLE distributors;

<varlistentry>

<term>

<synopsis>

ALTER TABLE <replaceable class="PARAMETER">table</replaceable>

DROP [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> { RESTRICT | CASCADE }

ALTER TABLE <replaceable class="PARAMETER">table</replaceable> DROP [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> { RESTRICT | CASCADE }

</synopsis>

</term>

<listitem>

<para>

Removes a column from a table.

If RESTRICT is specified only a column with no dependent

objects can be destroyed.

If CASCADE is specified, all objects that are dependent on

this column are also dropped.

</para>

<para>

Currently, to remove an existing column the table must be

recreated and reloaded:

<programlisting>

CREATE TABLE temp AS SELECT did, city FROM distributors;

DROP TABLE distributors;

</listitem>

</varlistentry>

</variablelist>

</para>

<para>

The clauses to rename columns and tables are <productname>PostgreSQL</productname>

extensions. SQL92 does not provide for them.

</para>

</refsect2>

</refsect1>

</refentry>