fix issue 609,610,611

[576470954]

What this PR does:
fix bug

Which issue(s) this PR fixes:

Fixes #609 #610 #611

Special notes for your reviewer:
about issue #611 , I found it have not release the conn, when the conn inited and not used(by condition cache have store the info)

Does this PR introduce a user-facing change?:

Fixes #609 #610 #611 

[576470954]

about issue #611 , may be close the conn at this position may be better

[codecov-commenter]

Codecov Report

Attention: 5 lines in your changes are missing coverage. Please review.

Comparison is base (c5fc98a) 37.28% compared to head (7a8b376) 37.28%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #612      +/-   ##
==========================================
- Coverage   37.28%   37.28%   -0.01%     
==========================================
  Files         175      175              
  Lines       11666    11667       +1     
==========================================
  Hits         4350     4350              
- Misses       6952     6953       +1     
  Partials      364      364              

Files	Coverage Δ
pkg/datasource/sql/conn_at.go	48.81% <0.00%> (-0.39%)	⬇️
...tasource/sql/exec/at/select_for_update_executor.go	30.23% <0.00%> (ø)

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[funky-eyes]

LGTM