双杠(||)在SQL中是什么意思? [英] What does double bars (||) mean in SQL?
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问题描述
我正在尝试理解以下查询:
select count(distinct Name || '' || Surname) from PEOPLE;
双杠是什么意思?该查询的作用是什么?
I'm trying to understand the following query:
select count(distinct Name || '' || Surname) from PEOPLE;
What does the double bars mean? What does this query do?
在MySQL中:
select "aaaaa" || '' || "bbbbb";
In MySQL:
select "aaaaa" || '' || "bbbbb";
+--------------------------+
| "aaaaa" || '' || "bbbbb" |
+--------------------------+
| 0 |
+--------------------------+
+--------------------------+
| "aaaaa" || '' || "bbbbb" |
+--------------------------+
| 0 |
+--------------------------+
推荐答案
双杠是隐喻的:
select 'hello' || ' ' || 'world' from dual;
收益
'hello world'
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