Constrain a table to only 1 row

I needed a table that could only ever have one row – if anyone tried to insert a second row they’d get an error.

CREATE UNIQUE INDEX only_one_row_allowed ON mytable (1);


Testing it:

INSERT INTO mytable VALUES ('x');
ORA-00001: unique constraint (SCOTT.ONLY_ONE_ROW_ALLOWED) violated


Jeffrey Kemp 21 March 2012

problem-solved / SQL / tips-&-tricks /

About Jeffrey Kemp

Application Designer & Developer at Oracle specialising in Oracle APEX (Application Express), Oracle SQL and PL/SQL. Oracle ACE Alumni ♠️. Piano player, father, husband, Christian. The views expressed on this blog are my own and do not necessarily reflect the views of Oracle.