dblink_build_sql_update
dblink_build_sql_update
dblink_build_sql_update - builds an UPDATE statement using a local tuple, replacing the primary key field values with alternative supplied values
Synopsis
dblink_build_sql_update(text relname,
int2vector primary_key_attnums,
integer num_primary_key_atts,
text[] src_pk_att_vals_array,
text[] tgt_pk_att_vals_array) returns text
Description
dblink_build_sql_update
can be useful in doing selective
replication of a local table to a remote database. It selects a row
from the local table based on primary key, and then builds an SQL
UPDATE
command that will duplicate that row, but with
the primary key values replaced by the values in the last argument.
(To make an exact copy of the row, just specify the same values for
the last two arguments.) The
UPDATE
command always assigns
all fields of the row - the main difference between this and
dblink_build_sql_insert
is that it's assumed that
the target row already exists in the remote table.
Arguments
-
relname -
Name of a local relation, for example
fooormyschema.mytab. Include double quotes if the name is mixed-case or contains special characters, for example"FooBar"; without quotes, the string will be folded to lower case. -
primary_key_attnums -
Attribute numbers (1-based) of the primary key fields, for example
1 2. -
num_primary_key_atts -
The number of primary key fields.
-
src_pk_att_vals_array -
Values of the primary key fields to be used to look up the local tuple. Each field is represented in text form. An error is thrown if there is no local row with these primary key values.
-
tgt_pk_att_vals_array -
Values of the primary key fields to be placed in the resulting
UPDATEcommand. Each field is represented in text form.
Return Value
Returns the requested SQL statement as text.
Notes
As of
PostgreSQL
9.0, the attribute numbers in
primary_key_attnums
are interpreted as logical
column numbers, corresponding to the column's position in
SELECT * FROM relname
. Previous versions interpreted the
numbers as physical column positions. There is a difference if any
column(s) to the left of the indicated column have been dropped during
the lifetime of the table.
Examples
SELECT dblink_build_sql_update('foo', '1 2', 2, '{"1", "a"}', '{"1", "b"}');
dblink_build_sql_update
-------------------------------------------------------------
UPDATE foo SET f1='1',f2='b',f3='1' WHERE f1='1' AND f2='b'
(1 row)