SQL> select 1 || 2 from dual; 1||2 ---- 12 SQL> select 1 || 'a' from dual; 1||'A' ------ 1a SQL> select 1 || "a" from dual; ORA-00904: "a": invalid identifier SQL> select (1 || 'a') 'c' from dual; ORA-00923: FROM keyword not found where expected SQL> select (1 || 'a') c from dual; C -- 1a SQL> select (1 || 'a') "c" from dual; c -- 1a
代码解析:
1:oracle 中字符串连接使用单引号;
2:oracle 中字符串给连接的字符串起别名要么加双引号,要么不加;