Postgresql 中文操作指南
dblink_build_sql_update
dblink_build_sql_update — 使用本地元组构建 UPDATE 语句，用备用提供的数值替换主键字段数值
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 textDescription
dblink_build_sql_update 可以帮助将本地表有目的地复制到远程数据库。它根据主键从本地表选择一行，然后构建一个 SQL UPDATE 命令，该命令将复制该行，但主键数值将替换为最后一个参数中的数值。（若要对该行进行完全复制，只需为最后两个参数指定相同的值即可。） UPDATE 命令始终分配该行的所有字段，其与 dblink_build_sql_insert 的主要区别在于它假设目标行已存在于远程表中。
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
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relname
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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.
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primary_key_attnums
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Attribute numbers (1-based) of the primary key fields, for example 1 2.
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num_primary_key_atts
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The number of primary key fields.
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src_pk_att_vals_array
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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.
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tgt_pk_att_vals_array
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Values of the primary key fields to be placed in the resulting UPDATE command. Each field is represented in text form.
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Notes
截至 PostgreSQL 9.0， primary_key_attnums 中的属性编号被解释为逻辑列编号，对应于该列在 SELECT * FROM relname 中的位置。以前版本将数字解释为物理列位置。如果在表的生命周期内删除了指示列左侧的任何列，则会有差异。
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.