`filed` to avoid the field conflict with mysql keyword

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (34687c6) 39.88% compared to head (7aaf513) 39.88%. Report is 1 commits behind head on master.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #125 +/- ## ======================================= Coverage 39.88% 39.88% ======================================= Files 22 22 Lines 2856 2856 ======================================= Hits 1139 1139 Misses 1717 1717 ``` | [Files](https://app.codecov.io/gh/qicosmos/ormpp/pull/125?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qicosmos) | Coverage Δ | | |---|---|---| | [include/utility.hpp](https://app.codecov.io/gh/qicosmos/ormpp/pull/125?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qicosmos#diff-aW5jbHVkZS91dGlsaXR5LmhwcA==) | `98.70% <100.00%> (ø)` | |

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