session: load variables before parsing SQL

[YangKeao]

What problem does this PR solve?

Issue Number: close #51387

Problem Summary:

The session variables are not loaded before parsing the SQL statements, which makes SQLMode incorrect.

What changed and how does it work?

Load session variables before parsing the statements.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.

Release note

Fix the issue that SQLMode doesn't have effect on the first statement in a session.

[tiprow]

@YangKeao: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
fast_test_tiprow	89a9b4b	link	true	/test fast_test_tiprow

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[codecov]

Codecov Report

Merging #51466 (89a9b4b) into master (1d24b1c) will increase coverage by 2.2015%.
Report is 37 commits behind head on master.
The diff coverage is 91.4285%.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #51466        +/-   ##
================================================
+ Coverage   70.6992%   72.9007%   +2.2015%     
================================================
  Files          1462       1463         +1     
  Lines        435224     442691      +7467     
================================================
+ Hits         307700     322725     +15025     
+ Misses       108234      99748      -8486     
- Partials      19290      20218       +928     

Flag	Coverage Δ
integration	49.3121% <50.0000%> (?)
unit	70.4547% <91.4285%> (-0.0451%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	53.9957% <ø> (ø)
parser	∅ <ø> (∅)
br	51.3708% <ø> (+5.5165%)	⬆️

[YangKeao]

/run-check-issue-triage-complete

[bb7133]

LGTM

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: bb7133, xhebox

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-03-04 09:01:47.216310997 +0000 UTC m=+71334.238557385: ☑️ agreed by xhebox.
• 2024-03-05 17:29:31.347643036 +0000 UTC m=+188198.369889424: ☑️ agreed by bb7133.