1DBLINK(3) PostgreSQL 12.2 Documentation DBLINK(3)
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6 dblink - executes a query in a remote database
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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 options=-csearch_path=',
51 'select proname, prosrc from pg_proc')
52 AS t1(proname name, prosrc text)
53 WHERE proname LIKE 'bytea%';
54 The “alias” part of the FROM clause must specify the column names and
56 types that the function will return. (Specifying column names in an
57 alias is actually standard SQL syntax, but specifying column types is a
58 PostgreSQL extension.) This allows the system to understand what *
59 should expand to, and what proname in the WHERE clause refers to, in
60 advance of trying to execute the function. At run time, an error will
61 be thrown if the actual query result from the remote database does not
62 have the same number of columns shown in the FROM clause. The column
63 names need not match, however, and dblink does not insist on exact type
64 matches either. It will succeed so long as the returned data strings
65 are valid input for the column type declared in the FROM clause.
66
68 A convenient way to use dblink with predetermined queries is to create
69 a view. This allows the column type information to be buried in the
70 view, instead of having to spell it out in every query. For example,
71 CREATE VIEW myremote_pg_proc AS
73 SELECT *
74 FROM dblink('dbname=postgres options=-csearch_path=',
75 'select proname, prosrc from pg_proc')
76 AS t1(proname name, prosrc text);
77 SELECT * FROM myremote_pg_proc WHERE proname LIKE 'bytea%';
79
81 SELECT * FROM dblink('dbname=postgres options=-csearch_path=',
82 'select proname, prosrc from pg_proc')
83 AS t1(proname name, prosrc text) WHERE proname LIKE 'bytea%';
84 proname | prosrc
85 ------------+------------
86 byteacat | byteacat
87 byteaeq | byteaeq
88 bytealt | bytealt
89 byteale | byteale
90 byteagt | byteagt
91 byteage | byteage
92 byteane | byteane
93 byteacmp | byteacmp
94 bytealike | bytealike
95 byteanlike | byteanlike
96 byteain | byteain
97 byteaout | byteaout
98 (12 rows)
99 SELECT dblink_connect('dbname=postgres options=-csearch_path=');
101 dblink_connect
102 ----------------
103 OK
104 (1 row)
105 SELECT * FROM dblink('select proname, prosrc from pg_proc')
107 AS t1(proname name, prosrc text) WHERE proname LIKE 'bytea%';
108 proname | prosrc
109 ------------+------------
110 byteacat | byteacat
111 byteaeq | byteaeq
112 bytealt | bytealt
113 byteale | byteale
114 byteagt | byteagt
115 byteage | byteage
116 byteane | byteane
117 byteacmp | byteacmp
118 bytealike | bytealike
119 byteanlike | byteanlike
120 byteain | byteain
121 byteaout | byteaout
122 (12 rows)
123 SELECT dblink_connect('myconn', 'dbname=regression options=-csearch_path=');
125 dblink_connect
126 ----------------
127 OK
128 (1 row)
129 SELECT * FROM dblink('myconn', 'select proname, prosrc from pg_proc')
131 AS t1(proname name, prosrc text) WHERE proname LIKE 'bytea%';
132 proname | prosrc
133 ------------+------------
134 bytearecv | bytearecv
135 byteasend | byteasend
136 byteale | byteale
137 byteagt | byteagt
138 byteage | byteage
139 byteane | byteane
140 byteacmp | byteacmp
141 bytealike | bytealike
142 byteanlike | byteanlike
143 byteacat | byteacat
144 byteaeq | byteaeq
145 bytealt | bytealt
146 byteain | byteain
147 byteaout | byteaout
148 (14 rows)
149PostgreSQL 12.2 2020 DBLINK(3)