MySQL 双杠 (||) 在 SQL 中是什么意思？
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What does double bars (||) mean in SQL?
提问by zer0uno
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?
我试图理解以下查询：
select count(distinct Name || '' || Surname) from PEOPLE;
双条是什么意思？这个查询有什么作用？
In MySQL:select "aaaaa" || '' || "bbbbb";
在 MySQL 中：select "aaaaa" || '' || "bbbbb";
+--------------------------+
| "aaaaa" || '' || "bbbbb" |
+--------------------------+
| 0 |
+--------------------------+
+--------------------------+
| "aaaaa" || '' || "bbbbb" |
+--------------------------+
| 0 |
+--------------------------+
回答by Andreas
double bars are concatination:
双条是串联的：
select 'hello' || ' ' || 'world' from dual;
yields
产量
'hello world'
