Clean up and test SQLTransforms

[philippjfr]

Adds some tests for SQLTransform components and cleans up the generated SQL queries.

[codecov-commenter]

Codecov Report

Merging #384 (110d03b) into master (bb827b4) will increase coverage by 0.21%.
The diff coverage is 97.91%.

@@            Coverage Diff             @@
##           master     #384      +/-   ##
==========================================
+ Coverage   67.25%   67.47%   +0.21%     
==========================================
  Files          72       73       +1     
  Lines        7976     8033      +57     
==========================================
+ Hits         5364     5420      +56     
- Misses       2612     2613       +1     

Impacted Files	Coverage Δ
lumen/pipeline.py	59.94% <50.00%> (+0.17%)	⬆️
lumen/tests/transforms/test_sql.py	100.00% <100.00%> (ø)
lumen/transforms/sql.py	94.28% <100.00%> (+1.65%)	⬆️
lumen/views/base.py	62.66% <0.00%> (+0.07%)	⬆️
lumen/base.py	83.54% <0.00%> (+0.43%)	⬆️

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[github-actions]

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