[MariaDB]Fix bug when table has same name constraints.

[k1LoW]

ref: #288

[codecov]

Codecov Report

Merging #294 (a136f06) into master (ec213c5) will decrease coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #294      +/-   ##
==========================================
- Coverage   66.51%   66.47%   -0.05%     
==========================================
  Files          25       25              
  Lines        4097     4101       +4     
==========================================
+ Hits         2725     2726       +1     
- Misses       1089     1091       +2     
- Partials      283      284       +1     

Impacted Files	Coverage Δ
drivers/mysql/mysql.go	68.68% <100.00%> (+0.30%)	⬆️
datasource/datasource.go	40.14% <0.00%> (-2.12%)	⬇️

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