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update table1 set a=decode('a','n','n','a');
update table1 set a=decode(a,'y','n','n','y');
SQL code:
SQL> insert into t55 values('n');
1 row inserted
SQL> update t55 set c1=decode(c1,'y','n','n','y');
2 rows updated
SQL> select * from t55;
C1
--
n
y
SQL> update t55 set c1=decode(c1,'y','n','n','y');
2 rows updated
SQL> select * from t55;
C1
--
y
n
SQL>
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update table1 set a=(case when a='y' then 'n' else 'y' end)
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