fix undo log sql type bug

[luky116]

What this PR does:

Which issue(s) this PR fixes:

Fixes #494

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[codecov-commenter]

Codecov Report

Merging #495 (2f5e103) into master (508795b) will increase coverage by 0.32%.
The diff coverage is 42.56%.

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@@            Coverage Diff             @@
##           master     #495      +/-   ##
==========================================
+ Coverage   38.73%   39.05%   +0.32%     
==========================================
  Files         149      152       +3     
  Lines        9980    10218     +238     
==========================================
+ Hits         3866     3991     +125     
- Misses       5794     5905     +111     
- Partials      320      322       +2     

Impacted Files	Coverage Δ
pkg/datasource/sql/at.go	0.00% <0.00%> (ø)
pkg/datasource/sql/exec/at/at_executor.go	0.00% <0.00%> (ø)
pkg/datasource/sql/exec/at/base_executor.go	39.13% <0.00%> (+1.18%)	⬆️
pkg/datasource/sql/exec/at/delete_executor.go	23.23% <0.00%> (ø)
pkg/datasource/sql/exec/at/insert_executor.go	42.03% <0.00%> (ø)
...atasource/sql/exec/at/insert_on_update_executor.go	38.41% <0.00%> (ø)
pkg/datasource/sql/exec/at/multi_executor.go	0.00% <0.00%> (ø)
pkg/datasource/sql/exec/at/multi_update_excutor.go	32.35% <0.00%> (ø)
...tasource/sql/exec/at/select_for_update_executor.go	30.23% <0.00%> (-0.58%)	⬇️
pkg/datasource/sql/exec/at/update_executor.go	25.00% <0.00%> (ø)
... and 13 more

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