1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
|
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>30.2.Connecting to the Database Server</title>
<link rel="stylesheet" href="stylesheet.css" type="text/css">
<link rev="made" href="pgsql-docs@postgresql.org">
<meta name="generator" content="DocBook XSL Stylesheets V1.70.0">
<link rel="start" href="index.html" title="PostgreSQL 8.1.4 Documentation">
<link rel="up" href="ecpg.html" title="Chapter30.ECPG - Embedded SQL in C">
<link rel="prev" href="ecpg.html" title="Chapter30.ECPG - Embedded SQL in C">
<link rel="next" href="ecpg-disconnect.html" title="30.3.Closing a Connection">
<link rel="copyright" href="ln-legalnotice.html" title="Legal Notice">
</head>
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="ecpg-connect"></a>30.2.Connecting to the Database Server</h2></div></div></div>
<p> One connects to a database using the following statement:
</p>
<pre class="programlisting">EXEC SQL CONNECT TO <em class="replaceable"><code>target</code></em> [<span class="optional">AS <em class="replaceable"><code>connection-name</code></em></span>] [<span class="optional">USER <em class="replaceable"><code>user-name</code></em></span>];</pre>
<p>
The <em class="replaceable"><code>target</code></em> can be specified in the
following ways:
</p>
<div class="itemizedlist"><ul type="disc">
<li> <code class="literal"><em class="replaceable"><code>dbname</code></em>[<span class="optional">@<em class="replaceable"><code>hostname</code></em></span>][<span class="optional">:<em class="replaceable"><code>port</code></em></span>]</code>
</li>
<li> <code class="literal">tcp:postgresql://<em class="replaceable"><code>hostname</code></em>[<span class="optional">:<em class="replaceable"><code>port</code></em></span>][<span class="optional">/<em class="replaceable"><code>dbname</code></em></span>][<span class="optional">?<em class="replaceable"><code>options</code></em></span>]</code>
</li>
<li> <code class="literal">unix:postgresql://<em class="replaceable"><code>hostname</code></em>[<span class="optional">:<em class="replaceable"><code>port</code></em></span>][<span class="optional">/<em class="replaceable"><code>dbname</code></em></span>][<span class="optional">?<em class="replaceable"><code>options</code></em></span>]</code>
</li>
<li> an SQL string literal containing one of the above forms
</li>
<li> a reference to a character variable containing one of the above forms (see examples)
</li>
<li> <code class="literal">DEFAULT</code>
</li>
</ul></div>
<p>
If you specify the connection target literally (that is, not
through a variable reference) and you don't quote the value, then
the case-insensitivity rules of normal SQL are applied. In that
case you can also double-quote the individual parameters separately
as needed. In practice, it is probably less error-prone to use a
(single-quoted) string literal or a variable reference. The
connection target <code class="literal">DEFAULT</code> initiates a connection
to the default database under the default user name. No separate
user name or connection name may be specified in that case.
</p>
<p> There are also different ways to specify the user name:
</p>
<div class="itemizedlist"><ul type="disc">
<li> <code class="literal"><em class="replaceable"><code>username</code></em></code>
</li>
<li> <code class="literal"><em class="replaceable"><code>username</code></em>/<em class="replaceable"><code>password</code></em></code>
</li>
<li> <code class="literal"><em class="replaceable"><code>username</code></em> IDENTIFIED BY <em class="replaceable"><code>password</code></em></code>
</li>
<li> <code class="literal"><em class="replaceable"><code>username</code></em> USING <em class="replaceable"><code>password</code></em></code>
</li>
</ul></div>
<p>
As above, the parameters <em class="replaceable"><code>username</code></em> and
<em class="replaceable"><code>password</code></em> may be an SQL identifier, an
SQL string literal, or a reference to a character variable.
</p>
<p> The <em class="replaceable"><code>connection-name</code></em> is used to handle
multiple connections in one program. It can be omitted if a
program uses only one connection. The most recently opened
connection becomes the current connection, which is used by default
when an SQL statement is to be executed (see later in this
chapter).
</p>
<p> Here are some examples of <code class="command">CONNECT</code> statements:
</p>
<pre class="programlisting">EXEC SQL CONNECT TO mydb@sql.mydomain.com;
EXEC SQL CONNECT TO 'unix:postgresql://sql.mydomain.com/mydb' AS myconnection USER john;
EXEC SQL BEGIN DECLARE SECTION;
const char *target = "mydb@sql.mydomain.com";
const char *user = "john";
EXEC SQL END DECLARE SECTION;
...
EXEC SQL CONNECT TO :target USER :user;</pre>
<p>
The last form makes use of the variant referred to above as
character variable reference. You will see in later sections how C
variables can be used in SQL statements when you prefix them with a
colon.
</p>
<p> Be advised that the format of the connection target is not
specified in the SQL standard. So if you want to develop portable
applications, you might want to use something based on the last
example above to encapsulate the connection target string
somewhere.
</p>
</div></body>
</html>
|
