opt: index accelerate chained fetch value operators

Prior to cockroachdb#55316, the optimizer generated inverted index scans on indexed
JSON columns when queries had filters with chained fetch value
operators, for example `j->'a'->'b' = '1'`. The logic that made this
possible was found to create query plans not equivalent to the query, so
it was removed. This commit restores the ability to index accelerate
chained -> operators.

Fixes cockroachdb#55317

Release note (performance improvement): A bug fix included in 20.2.1 for
for the JSON fetch value operator, `->`, resulted in chained `->`
operators in query filters not being index accelerated, e.g.,
`j->'a'->'b' = '1'`. Chained `->` are now index accelerated.

pkg/sql/logictest/testdata/logic_test/inverted_index

@@ -744,7 +744,15 @@ INSERT INTO f VALUES
   (2, '{"b": 2}'),
   (3, '{"b": 2, "a": 1}'),
   (4, '{"a": 1, "c": 3}'),
-  (5, '{"a": [1, 2]}')
+  (5, '{"a": [1, 2]}'),
+  (6, '{"a": {"b": 1}}'),
+  (7, '{"a": {"b": 1, "d": 2}}'),
+  (8, '{"a": {"d": 2}}'),
+  (9, '{"a": {"b": [1, 2]}}'),
+  (10, '{"a": {"b": {"c": 1}}}'),
+  (11, '{"a": {"b": {"c": 1, "d": 2}}}}'),
+  (12, '{"a": {"b": {"d": 2}}}}'),
+  (13, '{"a": {"b": {"c": [1, 2]}}}')
 
 query T
 SELECT j FROM f@i WHERE j->'a' = '1' ORDER BY k
@@ -769,6 +777,18 @@ SELECT j FROM f@i WHERE j->'a' = '1' OR j @> '{"b": 2}' ORDER BY k
 {"a": 1, "b": 2}
 {"a": 1, "c": 3}
 
+query T
+SELECT j FROM f@i WHERE j->'a'->'b' = '1' ORDER BY k
+----
+{"a": {"b": 1}}
+{"a": {"b": 1, "d": 2}}
+
+query T
+SELECT j FROM f@i WHERE j->'a'->'b'->'c' = '1' ORDER BY k
+----
+{"a": {"b": {"c": 1}}}
+{"a": {"b": {"c": 1, "d": 2}}}
+
 subtest arrays
 
 statement ok

pkg/sql/opt/exec/execbuilder/testdata/inverted_index

@@ -350,24 +350,23 @@ vectorized: true
       table: d@foo_inv
       spans: /"a"/"b"-/"a"/"b"/PrefixEnd
 
-# TODO(mgartner): Add support for building inverted index constraints for chained JSON
-# fetch operators.
 query T
-EXPLAIN (VERBOSE) SELECT * from d where b->'a'->'c' = '"b"'
+EXPLAIN (VERBOSE) SELECT * from d@foo_inv where b->'a'->'c' = '"b"'
 ----
 distribution: local
 vectorized: true
 ·
-• filter
+• index join
 │ columns: (a, b)
 │ estimated row count: 111 (missing stats)
-│ filter: ((b->'a')->'c') = '"b"'
+│ table: d@primary
+│ key columns: a
 │
 └── • scan
-      columns: (a, b)
-      estimated row count: 1,000 (missing stats)
-      table: d@primary
-      spans: FULL SCAN
+      columns: (a)
+      estimated row count: 111 (missing stats)
+      table: d@foo_inv
+      spans: /"a"/"c"/"b"-/"a"/"c"/"b"/PrefixEnd
 
 query T
 EXPLAIN (VERBOSE) SELECT * from d where b->(NULL::STRING) = '"b"'

pkg/sql/opt/invertedidx/json_array.go

@@ -334,35 +334,18 @@ func (j *jsonOrArrayFilterPlanner) extractJSONOrArrayContainsCondition(
 
 // extractJSONFetchValEqCondition extracts an InvertedExpression representing an
 // inverted filter over the planner's inverted index, based on equality between
-// a fetch val expression and a right scalar expression. If the following criteria
-// are not met, an empty InvertedExpression is returned.
+// a chain of fetch val expressions and a right scalar expression. If an
+// InvertedExpression cannot be generated from the expression, an
+// inverted.NonInvertedColExpression is returned.
 //
-//   1. The fetch value operator's left expression must be a variable
-//      referencing the inverted column in the index.
-//   2. The fetch value operator's right expression must be a constant string.
-//   3. The right expression in the equality expression must be a constant JSON
-//      value that is not an object or an array.
-//
-// TODO(mgartner): Support chained fetch val operators, e.g., j->'a'->'b' = '1'.
+// In order to generate an InvertedExpression, left must be a fetch val
+// expression in the form [col]->[index0]->[index1]->...->[indexN] where col is
+// a variable or expression referencing the inverted column in the inverted
+// index and each index is a constant string. The right expression must be a
+// constant JSON value that is not an object or an array.
 func (j *jsonOrArrayFilterPlanner) extractJSONFetchValEqCondition(
-	evalCtx *tree.EvalContext, fetch *memo.FetchValExpr, right opt.ScalarExpr,
+	evalCtx *tree.EvalContext, left *memo.FetchValExpr, right opt.ScalarExpr,
 ) inverted.Expression {
-	// The left side of the fetch val expression, the Json field, should be a
-	// variable corresponding to the index column.
-	if !isIndexColumn(j.tabID, j.index, fetch.Json, j.computedColumns) {
-		return inverted.NonInvertedColExpression{}
-	}
-
-	// The right side of the fetch val expression, the Index field, should be a
-	// constant string.
-	if !memo.CanExtractConstDatum(fetch.Index) {
-		return inverted.NonInvertedColExpression{}
-	}
-	key, ok := memo.ExtractConstDatum(fetch.Index).(*tree.DString)
-	if !ok {
-		return inverted.NonInvertedColExpression{}
-	}
-
 	// The right side of the equals expression should be a constant JSON value
 	// that is not an object or array.
 	if !memo.CanExtractConstDatum(right) {
@@ -377,10 +360,76 @@ func (j *jsonOrArrayFilterPlanner) extractJSONFetchValEqCondition(
 		return inverted.NonInvertedColExpression{}
 	}
 
-	// Build a new JSON object of the form: {<key>: <right>}.
-	b := json.NewObjectBuilder(1)
-	b.Add(string(*key), val.JSON)
-	obj := tree.NewDJSON(b.Build())
+	// Recursively traverse fetch val expressions and collect keys with which to
+	// build the InvertedExpression. If it is not possible to build an inverted
+	// expression from the tree of fetch val expressions, collectKeys returns
+	// early and foundKeys remains false. If successful, foundKeys is set to
+	// true and JSON fetch value indexes are collected in keys. The keys are
+	// ordered by the outer-most fetch val index first. The outer-most fetch val
+	// index is the right-most in the -> chain, for example (j->'a'->'b') is
+	// equivalent to ((j->'a')->'b') and 'b' is the outer-most fetch val index.
+	//
+	// Later on, we iterate forward through these keys to build a JSON object
+	// from the inside-out with the inner-most value being the JSON scalar
+	// extracted above from the right ScalarExpr function argument. In the
+	// resulting JSON object, the outer-most JSON fetch value indexes are the
+	// inner most JSON object keys.
+	//
+	// As an example, when left is (j->'a'->'b') and right is ('1'), the keys
+	// {"b", "a"} are collected and the JSON object {"a": {"b": 1}} is built.
+	foundKeys := false
+	var keys []string
+	var collectKeys func(fetch *memo.FetchValExpr)
+	collectKeys = func(fetch *memo.FetchValExpr) {
+		// The right side of the fetch val expression, the Index field, must be
+		// a constant string. If not, then we cannot build an inverted
+		// expression.
+		if !memo.CanExtractConstDatum(fetch.Index) {
+			return
+		}
+		key, ok := memo.ExtractConstDatum(fetch.Index).(*tree.DString)
+		if !ok {
+			return
+		}
+
+		// Append the key to the list of keys.
+		keys = append(keys, string(*key))
+
+		// If the left side of the fetch val expression, the Json field, is a
+		// variable or expression corresponding to the index column, then we
+		// have found a valid list of keys to build an inverted expression.
+		if isIndexColumn(j.tabID, j.index, fetch.Json, j.computedColumns) {
+			foundKeys = true
+			return
+		}
+
+		// If the left side of the fetch val expression is another fetch val
+		// expression, recursively collect its keys.
+		if innerFetch, ok := fetch.Json.(*memo.FetchValExpr); ok {
+			collectKeys(innerFetch)
+		}
+
+		// Otherwise, we cannot build an inverted expression.
+	}
+	collectKeys(left)
+	if !foundKeys {
+		return inverted.NonInvertedColExpression{}
+	}
+
+	// Build a new JSON object of the form:
+	//   {<keyN>: ... {<key1>: {key0: <val>}}}
+	// Note that key0 is the outer-most fetch val index, so the expression
+	// j->'a'->'b' = 1 results in {"a": {"b": 1}}.
+	var obj json.JSON
+	for i := 0; i < len(keys); i++ {
+		b := json.NewObjectBuilder(1)
+		if i == 0 {
+			b.Add(keys[i], val.JSON)
+		} else {
+			b.Add(keys[i], obj)
+		}
+		obj = b.Build()
+	}
 
-	return getInvertedExprForJSONOrArrayIndex(evalCtx, obj)
+	return getInvertedExprForJSONOrArrayIndex(evalCtx, tree.NewDJSON(obj))
 }

pkg/sql/opt/invertedidx/json_array_test.go

@@ -424,6 +424,33 @@ func TestTryFilterJsonOrArrayIndex(t *testing.T) {
 			indexOrd: arrayOrd,
 			ok:       false,
 		},
+		{
+			filters:  "j->'a'->'b' = '1'",
+			indexOrd: jsonOrd,
+			ok:       true,
+			tight:    true,
+			unique:   true,
+		},
+		{
+			filters:  "j->'a'->'b'->'c' = '1'",
+			indexOrd: jsonOrd,
+			ok:       true,
+			tight:    true,
+			unique:   true,
+		},
+		{
+			// Integer indexes are not yet supported.
+			filters:  "j->0->'b' = '1'",
+			indexOrd: jsonOrd,
+			ok:       false,
+		},
+		{
+			// The inner most expression is not a fetch val expression with an
+			// indexed column on the left.
+			filters:  "(j-'c')->'a'->'b' = '1'",
+			indexOrd: jsonOrd,
+			ok:       false,
+		},
 		{
 			filters:  "j->'a' = '1' AND j->'b' = '2'",
 			indexOrd: jsonOrd,

pkg/sql/opt/xform/testdata/rules/select

@@ -1951,6 +1951,20 @@ project
       │    └── spans: ["7a\x00\x01\x12b\x00\x01", "7a\x00\x01\x12b\x00\x01"]
       └── key: (1)
 
+# Chained fetch val operators.
+opt expect=GenerateInvertedIndexScans
+SELECT k FROM b WHERE j->'a'->'b' = '"c"'
+----
+project
+ ├── columns: k:1!null
+ ├── immutable
+ ├── key: (1)
+ └── scan b@j_inv_idx
+      ├── columns: k:1!null
+      ├── inverted constraint: /6/1
+      │    └── spans: ["7a\x00\x02b\x00\x01\x12c\x00\x01", "7a\x00\x02b\x00\x01\x12c\x00\x01"]
+      └── key: (1)
+
 # Do not generate an inverted scan when the fetch val and equality operators are
 # wrapped in a NOT operator. The -> operator returns NULL if the key does not
 # exist in the JSON object, so (NOT j->'a' = '"b"') is not equivalent to the