1DBLINK(3) PostgreSQL 9.2.24 Documentation DBLINK(3)
2
6 dblink - executes a query in a remote database
7
9 dblink(text connname, text sql [, bool fail_on_error]) returns setof record
10 dblink(text connstr, text sql [, bool fail_on_error]) returns setof record
11 dblink(text sql [, bool fail_on_error]) returns setof record
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14 dblink executes a query (usually a SELECT, but it can be any SQL
15 statement that returns rows) in a remote database.
16 When two text arguments are given, the first one is first looked up as
18 a persistent connection's name; if found, the command is executed on
19 that connection. If not found, the first argument is treated as a
20 connection info string as for dblink_connect, and the indicated
21 connection is made just for the duration of this command.
22
24 connname
25 Name of the connection to use; omit this parameter to use the
26 unnamed connection.
27 connstr
29 A connection info string, as previously described for
30 dblink_connect.
31 sql
33 The SQL query that you wish to execute in the remote database, for
34 example select * from foo.
35 fail_on_error
37 If true (the default when omitted) then an error thrown on the
38 remote side of the connection causes an error to also be thrown
39 locally. If false, the remote error is locally reported as a
40 NOTICE, and the function returns no rows.
41
43 The function returns the row(s) produced by the query. Since dblink can
44 be used with any query, it is declared to return record, rather than
45 specifying any particular set of columns. This means that you must
46 specify the expected set of columns in the calling query — otherwise
47 PostgreSQL would not know what to expect. Here is an example:
48 SELECT *
50 FROM dblink('dbname=mydb', 'select proname, prosrc from pg_proc')
51 AS t1(proname name, prosrc text)
52 WHERE proname LIKE 'bytea%';
53 The “alias” part of the FROM clause must specify the column names and
55 types that the function will return. (Specifying column names in an
56 alias is actually standard SQL syntax, but specifying column types is a
57 PostgreSQL extension.) This allows the system to understand what *
58 should expand to, and what proname in the WHERE clause refers to, in
59 advance of trying to execute the function. At run time, an error will
60 be thrown if the actual query result from the remote database does not
61 have the same number of columns shown in the FROM clause. The column
62 names need not match, however, and dblink does not insist on exact type
63 matches either. It will succeed so long as the returned data strings
64 are valid input for the column type declared in the FROM clause.
65
67 A convenient way to use dblink with predetermined queries is to create
68 a view. This allows the column type information to be buried in the
69 view, instead of having to spell it out in every query. For example,
70 CREATE VIEW myremote_pg_proc AS
72 SELECT *
73 FROM dblink('dbname=postgres', 'select proname, prosrc from pg_proc')
74 AS t1(proname name, prosrc text);
75 SELECT * FROM myremote_pg_proc WHERE proname LIKE 'bytea%';
77
79 SELECT * FROM dblink('dbname=postgres', 'select proname, prosrc from pg_proc')
80 AS t1(proname name, prosrc text) WHERE proname LIKE 'bytea%';
81 proname | prosrc
82 ------------+------------
83 byteacat | byteacat
84 byteaeq | byteaeq
85 bytealt | bytealt
86 byteale | byteale
87 byteagt | byteagt
88 byteage | byteage
89 byteane | byteane
90 byteacmp | byteacmp
91 bytealike | bytealike
92 byteanlike | byteanlike
93 byteain | byteain
94 byteaout | byteaout
95 (12 rows)
96 SELECT dblink_connect('dbname=postgres');
98 dblink_connect
99 ----------------
100 OK
101 (1 row)
102 SELECT * FROM dblink('select proname, prosrc from pg_proc')
104 AS t1(proname name, prosrc text) WHERE proname LIKE 'bytea%';
105 proname | prosrc
106 ------------+------------
107 byteacat | byteacat
108 byteaeq | byteaeq
109 bytealt | bytealt
110 byteale | byteale
111 byteagt | byteagt
112 byteage | byteage
113 byteane | byteane
114 byteacmp | byteacmp
115 bytealike | bytealike
116 byteanlike | byteanlike
117 byteain | byteain
118 byteaout | byteaout
119 (12 rows)
120 SELECT dblink_connect('myconn', 'dbname=regression');
122 dblink_connect
123 ----------------
124 OK
125 (1 row)
126 SELECT * FROM dblink('myconn', 'select proname, prosrc from pg_proc')
128 AS t1(proname name, prosrc text) WHERE proname LIKE 'bytea%';
129 proname | prosrc
130 ------------+------------
131 bytearecv | bytearecv
132 byteasend | byteasend
133 byteale | byteale
134 byteagt | byteagt
135 byteage | byteage
136 byteane | byteane
137 byteacmp | byteacmp
138 bytealike | bytealike
139 byteanlike | byteanlike
140 byteacat | byteacat
141 byteaeq | byteaeq
142 bytealt | bytealt
143 byteain | byteain
144 byteaout | byteaout
145 (14 rows)
146PostgreSQL 9.2.24 2017-11-06 DBLINK(3)