Sql 如何在Oracle中使用substr？

有一个表列消息值为

Command triggerEvent started
Command stopService stopped
Command startService started
Command executeCommand running
......

现在我想选择命令名，即triggerEvent、stopService、startService

我尝试使用oracle substr和instr获取它们，但失败了

select substr(message, instr(message, ' ')) from event

---

有什么好办法吗？

您可以使用REGEXP\u SUBSTR使用更短的代码

比如说,

SQL> WITH sample_data AS(
  2  SELECT 'Command triggerEvent started' str FROM dual UNION ALL
  3  SELECT 'Command stopService stopped' str FROM dual UNION ALL
  4  SELECT 'Command startService started' str FROM dual UNION ALL
  5  SELECT 'Command executeCommand running' str FROM dual
  6  )
  7  -- end of sample_data mocking as real table
  8  SELECT trim(regexp_substr(str, '[^ ]+', 1, 2)) command
  9  FROM sample_data;

COMMAND
------------------------------
triggerEvent
stopService
startService
executeCommand

当然，最好使用SUBSTR和INSTR，因为它们的CPU密集度比正则表达式的速度要低

SQL> WITH sample_data AS(
  2  SELECT 'Command triggerEvent started' str FROM dual UNION ALL
  3  SELECT 'Command stopService stopped' str FROM dual UNION ALL
  4  SELECT 'Command startService started' str FROM dual UNION ALL
  5  SELECT 'Command executeCommand running' str FROM dual
  6  )
  7  -- end of sample_data mocking as real table
  8  SELECT trim(SUBSTR(str, instr(str, ' ', 1, 1),
  9                     instr(str, ' ', 1, 2) - instr(str, ' ', 1, 1))
 10              ) command
 11  FROM sample_data;

COMMAND
------------------------------
triggerEvent
stopService
startService
executeCommand

---

这将为您提供消息中的第二个单词

with event(message) as (
select 'command triggerEvent started' from dual union
select 'Command stopService stopped' from dual) --recreate table

--query start
select trim(regexp_substr(message,'[[:alpha:]]+ ',1,2)) command FROM event

---

正则表达式的问题在于它取决于[[：alpha:]]字符类，如果命令包含字母表以外的字符，该怎么办。结果将为空。与其依赖字符串，不如使用分隔符。你是对的。但是OP给出的示例没有非字母数字字符。但是，是的，最好是安全的谢谢你指出这一点