Simplify coalesce expressions #12192

Praveen2112 · 2019-01-08T10:18:39Z

For coalesce expression like coalesce(colA, colA) can be simplified to colA and for expressions like coalesce('1', colA) can be simplified to '1'. This patch captures those pattern and simplifies them. Also updated the test for the above changes

presto-main/src/main/java/com/facebook/presto/sql/planner/ExpressionInterpreter.java

presto-main/src/test/java/com/facebook/presto/sql/TestExpressionInterpreter.java

Praveen2112 · 2019-01-08T10:53:51Z

@kokosing Have added support for nested coalesce expressions.

kokosing · 2019-01-08T12:41:19Z

@sopel39 Would you like to take a look also?

sopel39 · 2019-01-08T12:54:50Z

presto-main/src/main/java/com/facebook/presto/sql/planner/ExpressionInterpreter.java

@@ -546,19 +548,38 @@ protected Object visitCoalesceExpression(CoalesceExpression node, Object context
            List<Object> values = node.getOperands().stream()
                    .map(value -> processWithExceptionHandling(value, context))
                    .filter(Objects::nonNull)
+                    .flatMap(expression -> {
+                        if (expression instanceof CoalesceExpression) {
+                            return ((CoalesceExpression) expression).getOperands().stream();


what if there are more levels of recursion? Make it recursive

But the current model is recursive right. We have added tests with more levels of coalesce and it passed it.

It only supports one level of recursion.

Won't ExpressionInterpreter#processWithExceptionHandling will call other levels ? We just need to check if one of argument is of CoalesceExpression If yes we will extract its arguments and push it to the outer expression and processWithExceptionHandling will ideally handle at more levels

If I am not wrong recursive implementation will simplify
coalesce(coalesce(unbound_long, coalesce(unbound_long, 1)), unbound_long2) to coalesce(unbound_long, 1)

Right, thanks

Sorry I have replaced it with isDeterministic((CoalesceExpression) expression)

I mean I think that isDeterministic((CoalesceExpression) expression) can be removed completely. We don't need to check if nested coalesce is deterministic

But in that case it will simplify coalesce(unbound_long, coalesce(random(), 1) to coalesce(unbound_long, random(), 1).

@sopel39 Removed the deterministic check as it is not required now

Thank you. Ping us when release is done to land it

presto-main/src/main/java/com/facebook/presto/sql/planner/ExpressionInterpreter.java

findepi · 2019-01-08T13:41:45Z

@Praveen2112 this will help a bit with #12155 (as per #12155 (comment)). Nice

Praveen2112 · 2019-01-08T13:44:39Z

@findepi I guess this one #12193 would also help the above issue.

sopel39 · 2019-01-09T10:26:50Z

presto-main/src/main/java/com/facebook/presto/sql/planner/ExpressionInterpreter.java

@@ -546,19 +548,38 @@ protected Object visitCoalesceExpression(CoalesceExpression node, Object context
            List<Object> values = node.getOperands().stream()
                    .map(value -> processWithExceptionHandling(value, context))
                    .filter(Objects::nonNull)
+                    .flatMap(expression -> {
+                        if (expression instanceof CoalesceExpression) {
+                            return ((CoalesceExpression) expression).getOperands().stream();


Right, thanks

presto-main/src/main/java/com/facebook/presto/sql/planner/ExpressionInterpreter.java

highker · 2019-02-23T01:24:53Z

Merged

facebook-github-bot added the CLA Signed label Jan 8, 2019

kokosing reviewed Jan 8, 2019

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Praveen2112 force-pushed the simplify_coalesce_expression branch from 0cb5678 to 7f0e4ad Compare January 8, 2019 10:51

Praveen2112 force-pushed the simplify_coalesce_expression branch from 7f0e4ad to 3dd19a7 Compare January 8, 2019 12:01

kokosing approved these changes Jan 8, 2019

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sopel39 reviewed Jan 8, 2019

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findepi mentioned this pull request Jan 8, 2019

Optimize plan created for join with USING clause #12193

Closed

Praveen2112 force-pushed the simplify_coalesce_expression branch from 3dd19a7 to fe3ef94 Compare January 8, 2019 17:14

sopel39 approved these changes Jan 9, 2019

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Praveen2112 force-pushed the simplify_coalesce_expression branch 2 times, most recently from 6f1e657 to 0993125 Compare January 9, 2019 17:27

Praveen2112 mentioned this pull request Jan 10, 2019

[WIP] : Simplify Coalesce for equivalent expressions #12206

Closed

Praveen2112 force-pushed the simplify_coalesce_expression branch 2 times, most recently from b843fa2 to 8fc124b Compare January 11, 2019 17:00

Simplify coalesce expressions

2803ca6

Praveen2112 force-pushed the simplify_coalesce_expression branch from 8fc124b to 2803ca6 Compare January 12, 2019 00:26

martint added the ready-to-merge label Jan 15, 2019

Praveen2112 mentioned this pull request Jan 24, 2019

Simplify coalesce expressions trinodb/trino#35

Merged

highker self-assigned this Feb 19, 2019

highker closed this Feb 23, 2019

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Simplify coalesce expressions #12192

Simplify coalesce expressions #12192

Praveen2112 commented Jan 8, 2019

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highker commented Feb 23, 2019

Simplify coalesce expressions #12192

Simplify coalesce expressions #12192

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