SQL Oracle 中的字符串连接运算符是什么？
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What is the string concatenation operator in Oracle?
提问by AJ.
What is the string concatenation operator in Oracle SQL?
Oracle SQL 中的字符串连接运算符是什么？
Are there any "interesting" features I should be careful of?
有什么我应该注意的“有趣”功能吗？
(This seems obvious, but I couldn't find a previous question asking it).
（这似乎很明显，但我找不到之前提出的问题）。
回答by Tony Andrews
It is ||, for example:
这是||，例如：
select 'Mr ' || ename from emp;
The only "interesting" feature I can think of is that 'x' || nullreturns 'x', not nullas you might perhaps expect.
我能想到的唯一“有趣”功能是'x' || null返回'x'，而不是null您可能期望的那样。
回答by Gary Myers
There's also concat, but it doesn't get used much
还有 concat，不过用的不多
select concat('a','b') from dual;
回答by Fabio Fantoni
I would suggest concat when dealing with 2 strings, and || when those strings are more than 2:
在处理 2 个字符串时，我建议使用 concat，而 || 当这些字符串大于 2 时：
select concat(a,b)
from dual
or
或者
select 'a'||'b'||'c'||'d'
from dual
回答by Ankur
DECLARE
a VARCHAR2(30);
b VARCHAR2(30);
c VARCHAR2(30);
BEGIN
a := ' Abc ';
b := ' def ';
c := a || b;
DBMS_OUTPUT.PUT_LINE(c);
END;
output:: Abc def
输出:: Abc def
回答by Grant Shannon
Using CONCAT(CONCAT(,),)worked for me when concatenating more than two strings.
CONCAT(CONCAT(,),)连接两个以上的字符串时，使用对我有用。
My problem required working with date strings (only) and creating YYYYMMDDfrom YYYY-MM-DDas follows (i.e. without converting to date format):
我的问题需要使用日期字符串（仅）并YYYYMMDD从YYYY-MM-DD以下创建（即不转换为日期格式）：
CONCAT(CONCAT(SUBSTR(DATECOL,1,4),SUBSTR(DATECOL,6,2)),SUBSTR(DATECOL,9,2)) AS YYYYMMDD
