Provide a FORCE NULL option to COPY in CSV mode.

This forces an input field containing the quoted null string to be
returned as a NULL. Without this option, only unquoted null strings
behave this way. This helps where some CSV producers insist on quoting
every field, whether or not it is needed. The option takes a list of
fields, and only applies to those columns. There is an equivalent
column-level option added to file_fdw.

Ian Barwick, with some tweaking by Andrew Dunstan, reviewed by Payal
Singh.

2 files changed, 36 insertions, 4 deletions

diff --git a/doc/src/sgml/file-fdw.sgml b/doc/src/sgml/file-fdw.sgml
index 9385b26d34d..d3b39aa120b 100644
--- a/doc/src/sgml/file-fdw.sgml
+++ b/doc/src/sgml/file-fdw.sgml
@@ -112,11 +112,11 @@
  </variablelist>
 
  <para>
-  Note that while <command>COPY</> allows options such as OIDS and HEADER 
+  Note that while <command>COPY</> allows options such as OIDS and HEADER
   to be specified without a corresponding value, the foreign data wrapper
-  syntax requires a value to be present in all cases.  To activate 
+  syntax requires a value to be present in all cases.  To activate
   <command>COPY</> options normally supplied without a value, you can
-  instead pass the value TRUE. 
+  instead pass the value TRUE.
  </para>
 
  <para>
@@ -140,6 +140,21 @@
    </listitem>
   </varlistentry>
 
+  <varlistentry>
+   <term><literal>force_null</literal></term>
+
+   <listitem>
+    <para>
+     This is a Boolean option.  If true, it specifies that values of the
+     column which match the null string are returned as <literal>NULL</>
+     even if the value is quoted. Without this option, only unquoted
+     values matching the null string are returned as <literal>NULL</>.
+     This has the same effect  as listing the column in
+     <command>COPY</>'s <literal>FORCE_NULL</literal> option.
+    </para>
+   </listitem>
+  </varlistentry>
+
  </variablelist>
 
  <para>
diff --git a/doc/src/sgml/ref/copy.sgml b/doc/src/sgml/ref/copy.sgml
index 99f246af171..5be3514612e 100644
--- a/doc/src/sgml/ref/copy.sgml
+++ b/doc/src/sgml/ref/copy.sgml
@@ -42,6 +42,7 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
     ESCAPE '<replaceable class="parameter">escape_character</replaceable>'
     FORCE_QUOTE { ( <replaceable class="parameter">column_name</replaceable> [, ...] ) | * }
     FORCE_NOT_NULL ( <replaceable class="parameter">column_name</replaceable> [, ...] )
+    FORCE_NULL ( <replaceable class="parameter">column_name</replaceable> [, ...] )
     ENCODING '<replaceable class="parameter">encoding_name</replaceable>'
 </synopsis>
  </refsynopsisdiv>
@@ -329,6 +330,20 @@ COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable
    </varlistentry>
 
    <varlistentry>
+    <term><literal>FORCE_NULL</></term>
+    <listitem>
+     <para>
+      Match the specified columns' values against the null string, even
+      if it has been quoted, and if a match is found set the value to
+      <literal>NULL</>. In the default case where the null string is empty,
+      this converts a quoted empty string into NULL.
+      This option is allowed only in <command>COPY FROM</>, and only when
+      using <literal>CSV</> format.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
     <term><literal>ENCODING</></term>
     <listitem>
      <para>
@@ -637,7 +652,9 @@ COPY <replaceable class="parameter">count</replaceable>
     string, while an empty string data value is written with double quotes
     (<literal>""</>). Reading values follows similar rules. You can
     use <literal>FORCE_NOT_NULL</> to prevent <literal>NULL</> input
-    comparisons for specific columns.
+    comparisons for specific columns. You can also use
+    <literal>FORCE_NULL</> to convert quoted null string data values to
+    <literal>NULL</>.
    </para>
 
    <para>