Projection Pushdown
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Definition
By enabling Projection Pushdown rule, PawSQL eliminates the columns in derived tables, common table expressions and views(after resolving), which are not referenced in outer query blocks, to:
- reduce the IO cost
- reduce the network cost
- enable index recommendation of index-only strategy
This justification is similar to rule [RuleStarInSelectList], but PawSQL supplies a rewrite optimization instead of only warning for star in select list scenario.
We will use derived table in following paragraph, but all the descriptions also apply to common table expressions and resolved views.