DBLINK_BUILD_SQL_UPDATE(3)        PostgreSQL 12.3 Documentation        DBLINK_BUILD_SQL_UPDATE(3)



NAME
       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 a 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 foo or myschema.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 UPDATE command. 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)



PostgreSQL 12.3                                2020                    DBLINK_BUILD_SQL_UPDATE(3)