What is the string concatenation operator in Oracle?

2018-06-30 00:05:25

What is the string concatenation operator in Oracle SQL?

Are there any "interesting" features I should be careful of?

(This seems obvious, but I couldn't find a previous question asking it).

It is || , for example:

select 'Mr ' || ename from emp;

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

还有concat，但没有太多用处

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

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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