What is the string concatenation operator in Oracle?

It is ||, for example:

select 'Mr ' || ename from emp;

The only "interesting" feature I can think of is that 'x' || null returns 'x', not null as you might perhaps expect.

sql oracle plsql string-concatenation

There's also concat, but it doesn't get used much

select concat('a','b') from dual;

sql oracle plsql string-concatenation

I would suggest concat when dealing with 2 strings, and || when those strings are more than 2:

select concat(a,b)  from dual

  select 'a'||'b'||'c'||'d'        from dual

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