expression, plan: aggressive constant fold for null parameter expression to simplify outer join#7696
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only do null fold in null reject check
plan cache test should pass now, reopen it
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| if !hasNullArg || !sc.InNullRejectCheck { | ||
| return expr, isDeferredConst | ||
| } | ||
| dummyScalarFunc, _ := x.Clone().(*ScalarFunction) |
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Can we use NewFunction instead?
| if !canFold { | ||
| return expr, isDeferredConst | ||
| if len(nonConstArgIdx) > 0 { | ||
| if !hasNullArg || !sc.InNullRejectCheck { |
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Do we need to check whether it's in null-reject?
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Yes we need, for cases like select null and a < 1 from t;, if we fold null constant for the projection part, the result would be null for all rows, but actually for t.a >= 1, the result should be 0
fold null if result is null or false
| UseCache bool | ||
| PadCharToFullLength bool | ||
| BatchCheck bool | ||
| InNullRejectCheck bool |
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Can we make this an input parameter for foldConstant?
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If we make it a parameter of foldConstant, we have to modify signature of FoldConstant, NewFunction, NewFunctionInternal, EvaluateExprWithNull, this would lead to a lot of unnecessary code changes
| if argIsConst[i] { | ||
| constArgs[i] = arg | ||
| } else { | ||
| constArgs[i] = One |
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Would it be incorrect if the ScalarFunction is NullEQ?
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is null and is not null should have only one parameter, so they would not fall into code path of this patch IMHO.
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What I mentioned here is the operator <=>.
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Oh you are right, will fix this, thanks.
| { | ||
| sql: "select * from t as t1 left join t as t2 on t1.b = t2.b where (t1.a=1 and t2.a=1) or (t1.a=2 and t2.a=2)", | ||
| sel: "[or(and(eq(t1.a, 1), eq(t2.a, 1)), and(eq(t1.a, 2), eq(t2.a, 2)))]", | ||
| sql: "select * from t as t1 left join t as t2 on t1.b = t2.b where (t1.a=1 and t2.a is null) or (t1.a=2 and t2.a=2)", |
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The purpose of this test case is to verify predicate pushdown over outer join, after applying this PR, the outer join would be converted to inner join now, so I changed the where condition to keep the outer join.
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| if !conOK { | ||
| canFold = false | ||
| con, conOK := foldedArg.(*Constant) | ||
| if conOK { |
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how about:
argIsConst[i] = conOk
allConstArg = allConstArg && conOk
hasNullArg = hasNullArg || (conOk && con.Value.IsNull())Maybe this is more clearer.
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thanks, patch updated
| if x.Value.IsNull() { | ||
| return true | ||
| } else if isTrue, err := x.Value.ToBool(sc); err != nil || isTrue == 0 { | ||
| } else if isTrue, err := x.Value.ToBool(sc); err == nil && isTrue == 0 { |
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should it be err == nil && isTrue != 0?
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isTrue != 0 means the where condition is true if the inner table columns are null, so it cannot be rejected?
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What problem does this PR solve?
Fix #7679
Currently,
foldConstantonly handles expressions likeconstant op constant, for expressions likeconstant op column, it does nothing. Actually, ifconstantinconstant op columnisnull, for a lot of operators, this expression can be folded intonull. This PR works on this enhancement.What is changed and how it works?
Substitute
expressioninconstant op expressionto constantOneif theconstantisnull, and evaluate the new expression. If the result isnull, we can fold this expression, otherwise, keep the original expression.Check List
Tests
Side effects