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PostgreSQL documentation

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whatever is in the table already).

</para>

<para>

When using the optional column list syntax, <command>COPY TO</command>

and <command>COPY FROM</command> willonly copy the specified

columns' values to/fromthe table. If a column in the table

is not in the column list,<command>COPY FROM</command> will insert

default values forthat column if a default value is defined.

<para>

If a list of columns is specified, <command>COPY</command>will

only copy thedata in thespecified columns to or from the table.

If there are any columns inthe table that are not in the table,

<command>COPY FROM</command> will insertthe default value for

that column.

</para>

<para>

</para>

<para>

<command>COPY FROM</command>neither invokes rules nor acts on column

defaults. It doesinvoketriggers and check constraints.

<command>COPY FROM</command>will invoke any triggers or check

constraints. However, it will notinvokerules.

</para>

<para>

The attribute values themselves are strings generated by the

output function, or acceptable to the input function, of each

attribute's data type. The specified null-value string is used in

place of attributes that are NULL.

place of attributes that are NULL. When using <command>COPY

FROM</command> without a column list, each row of the input file

must contain data for each attribute in the table: no missing data

is allowed. Similarly, <command>COPY FROM</command> will raise

an error if it encounters any data in the input file that would

not be inserted into the table: extra data is not allowed.

</para>

<para>

If OIDS is specified, the OID is read or written as the first column,