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Add error_on_null(), checking if the input is the null value

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This polymorphic function produces an error if the input value is
detected as being the null value; otherwise it returns the input value
unchanged.

This function can for example become handy in SQL function bodies, to
enforce that exactly one row was returned.

Author: Joel Jacobson <joel@compiler.org>
Reviewed-by: Vik Fearing <vik@postgresfriends.org>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/ece8c6d1-2ab1-45d5-ba12-8dec96fc8886@app.fastmail.com
Discussion: https://postgr.es/m/de94808d-ed58-4536-9e28-e79b09a534c7@app.fastmail.com
This commit is contained in:
Michael Paquier
2025-10-22 09:55:17 +09:00
parent 2470ca435c
commit 2b75c38b70
5 changed files with 81 additions and 0 deletions
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22
doc/src/sgml/func/func-comparison.sgml
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@@ -599,6 +599,28 @@ SELECT NOT(ROW(table.*) IS NOT NULL) FROM TABLE; -- detect at least one null in
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>error_on_null</primary>
</indexterm>
<function>error_on_null</function> ( <type>anyelement</type> )
<returnvalue>anyelement</returnvalue>
</para>
<para>
Checks if the input is the null value, generating an error if so;
otherwise, returns the input.
</para>
<para>
<literal>error_on_null(42)</literal>
<returnvalue>42</returnvalue>
</para>
<para>
<literal>error_on_null(row(null,null))</literal>
<returnvalue>(,)</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>