During online export (SELECT INTO), when quote='#', # in the string will not be escaped

**Bug Description**
During online export, when quote='#', the # in the string will not be escaped, which will lead to inconsistency when the exported data is imported again

**Expected Behavior**
```
Original data：~!@$%^#&*()_+<
After export：#~!@$%^#&*()_+<#
Expected：#~!@$%^\#&*()_+<#
```
**Relation Case**
test_select_into_load_data.yaml id:0-1
**Steps to Reproduce**

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Look at the online export logic, likely in a file handling SELECT INTO with quote characters. The test case test_select_into_load_data.yaml id:0-1 is a starting point. Understand how escaping works when quote='#' and ensure # in string data is escaped. Verify by running the test after changes.

Written by the indexing model from the issue text.