single row implied aggregates default to values instead of records

cmd/zed/manage/ztests/index.yaml

@@ -22,4 +22,4 @@ inputs:
 outputs:
   - name: stdout
     data: |
-      {count:10(uint64)}
+      10(uint64)

cmd/zed/ztests/query-stats.yaml

@@ -3,7 +3,7 @@ script: |
   zed init -q
   zed create -q test
   zed load -q -use test babble.zson
-  zed query -s -Z "from test | count()"
+  zed query -s -z "from test | count()"
 
 inputs:
   - name: babble.zson
@@ -12,9 +12,7 @@ inputs:
 outputs:
   - name: stdout
     data: |
-      {
-          count: 1000 (uint64)
-      }
+      1000(uint64)
   - name: stderr
     data: |
       {bytes_read:32889,bytes_matched:32889,records_read:1000,records_matched:1000}

cmd/zq/ztests/aggmem.yaml

@@ -10,7 +10,7 @@ inputs:
 outputs:
   - name: stdout
     data: |
-      {collect:null}
+      null
   - name: stderr
     data: |
       aggmem value must be greater than zero

cmd/zq/ztests/http-simple.yaml

@@ -10,4 +10,4 @@ inputs:
 outputs:
   - name: stdout
     data: |
-      {count:1000(uint64)}
+      1000(uint64)

cmd/zq/ztests/s3-parquet.yaml

@@ -12,4 +12,4 @@ inputs:
 outputs:
   - name: stdout
     data: |
-      {count:10(uint64)}
+      10(uint64)

cmd/zq/ztests/s3-simple.yaml

@@ -12,4 +12,4 @@ inputs:
 outputs:
   - name: stdout
     data: |
-      {count:1000(uint64)}
+      1000(uint64)

compiler/parser/ztests/summarize.yaml

@@ -8,4 +8,4 @@ input: |
 output-flags: -pretty=0
 
 output: |
-  {count:2(uint64)}
+  2(uint64)

compiler/parser/ztests/where-expr.yaml

@@ -13,6 +13,6 @@ inputs:
 outputs:
   - name: stdout
     data: |
-      {count:2(uint64)}
+      2(uint64)
       ===
-      {count:2(uint64)}
+      2(uint64)

compiler/parser/ztests/where-search.yaml

@@ -15,6 +15,6 @@ inputs:
 outputs:
   - name: stdout
     data: |
-      {count:2(uint64)}
+      2(uint64)
       ===
-      {count:2(uint64)}
+      2(uint64)

compiler/semantic/op.go

@@ -307,6 +307,11 @@ func semOp(ctx context.Context, scope *Scope, o ast.Op, ds *data.Source, head *l
 		if err != nil {
 			return nil, err
 		}
+		if len(keys) == 0 && len(o.Aggs) == 1 {
+			if op := singletonAgg(scope, o.Aggs[0]); op != nil {
+				return op, nil
+			}
+		}
 		aggs, err := semAssignments(scope, o.Aggs, true)
 		if err != nil {
 			return nil, err
@@ -629,6 +634,34 @@ func semOver(ctx context.Context, scope *Scope, in *ast.Over, ds *data.Source, h
 	}, nil
 }
 
+func singletonAgg(scope *Scope, agg ast.Assignment) dag.Op {
+	if agg.LHS != nil {
+		return nil
+	}
+	out, err := semAssignment(scope, agg, true)
+	if err != nil {
+		return nil
+	}
+	yield := &dag.Yield{
+		Kind: "Yield",
+	}
+	this, ok := out.LHS.(*dag.This)
+	if !ok || len(this.Path) != 1 {
+		return nil
+	}
+	yield.Exprs = append(yield.Exprs, this)
+	return &dag.Sequential{
+		Kind: "Sequential",
+		Ops: []dag.Op{
+			&dag.Summarize{
+				Kind: "Summarize",
+				Aggs: []dag.Assignment{out},
+			},
+			yield,
+		},
+	}
+}
+
 func semDecls(scope *Scope, decls []ast.Decl) ([]dag.Def, []*dag.Func, error) {
 	var consts []dag.Def
 	var fds []*ast.FuncDecl
@@ -804,7 +837,7 @@ func isBool(e dag.Expr) bool {
 
 func semCallOp(scope *Scope, call *ast.Call) (dag.Op, error) {
 	if agg, err := maybeConvertAgg(scope, call); err == nil && agg != nil {
-		return &dag.Summarize{
+		summarize := &dag.Summarize{
 			Kind: "Summarize",
 			Aggs: []dag.Assignment{
 				{
@@ -813,6 +846,14 @@ func semCallOp(scope *Scope, call *ast.Call) (dag.Op, error) {
 					RHS:  agg,
 				},
 			},
+		}
+		yield := &dag.Yield{
+			Kind:  "Yield",
+			Exprs: []dag.Expr{&dag.This{Kind: "This", Path: field.New(call.Name)}},
+		}
+		return &dag.Sequential{
+			Kind: "Sequential",
+			Ops:  []dag.Op{summarize, yield},
 		}, nil
 	}
 	if !function.HasBoolResult(call.Name) {

compiler/ztests/from-fork.yaml

@@ -9,5 +9,5 @@ inputs:
 outputs:
   - name: stdout
     data: |
-      {count:2(uint64)}
-      {count:2(uint64)}
+      2(uint64)
+      2(uint64)

docs/language/aggregates/and.md

@@ -18,7 +18,7 @@ echo 'true false true' | zq -z 'and(this)' -
 ```
 =>
 ```mdtest-output
-{and:false}
+false
 ```
 
 Continuous AND of simple sequence:

docs/language/aggregates/any.md

@@ -19,7 +19,7 @@ echo '1 2 3 4' | zq -z 'any(this)' -
 ```
 =>
 ```mdtest-output
-{any:1}
+1
 ```
 
 Continuous any over a simple sequence:
@@ -39,5 +39,5 @@ echo '"foo" 1 2 3 ' | zq -z 'any(this)' -
 ```
 =>
 ```mdtest-output
-{any:"foo"}
+"foo"
 ```

docs/language/aggregates/avg.md

@@ -18,7 +18,7 @@ echo '1 2 3 4' | zq -z 'avg(this)' -
 ```
 =>
 ```mdtest-output
-{avg:2.5}
+2.5
 ```
 
 Continuous average of simple sequence:
@@ -38,5 +38,5 @@ echo '1 2 3 4 "foo"' | zq -z 'avg(this)' -
 ```
 =>
 ```mdtest-output
-{avg:2.5}
+2.5
 ```

docs/language/aggregates/collect.md

@@ -20,7 +20,7 @@ echo '1 2 3 4' | zq -z 'collect(this)' -
 ```
 =>
 ```mdtest-output
-{collect:[1,2,3,4]}
+[1,2,3,4]
 ```
 
 Continuous collection over a simple sequence:
@@ -40,5 +40,5 @@ echo '1 2 3 4 "foo"' | zq -z 'collect(this)' -
 ```
 =>
 ```mdtest-output
-{collect:[1,2,3,4,"foo"]}
+[1,2,3,4,"foo"]
 ```

docs/language/aggregates/count.md

@@ -18,7 +18,7 @@ echo '1 2 3' | zq -z 'count()' -
 ```
 =>
 ```mdtest-output
-{count:3(uint64)}
+3(uint64)
 ```
 
 Continuous count of simple sequence:

docs/language/aggregates/dcount.md

@@ -19,7 +19,7 @@ echo '1 2 2 3' | zq -z 'dcount(this)' -
 ```
 =>
 ```mdtest-output
-{dcount:3(uint64)}
+3(uint64)
 ```
 
 Continuous count of simple sequence:

docs/language/aggregates/fuse.md

@@ -23,7 +23,7 @@ echo '{a:1,b:2}{a:2,b:"foo"}' | zq -z 'fuse(this)' -
 ```
 =>
 ```mdtest-output
-{fuse:<{a:int64,b:(int64,string)}>}
+<{a:int64,b:(int64,string)}>
 ```
 Fuse records with a group-by key:
 ```mdtest-command

docs/language/aggregates/map.md

@@ -21,7 +21,7 @@ echo '{stock:"APPL",price:145.03} {stock:"GOOG",price:87.07}' | zq -z 'map(|{sto
 ```
 =>
 ```mdtest-output
-{map:|{"APPL":145.03,"GOOG":87.07}|}
+|{"APPL":145.03,"GOOG":87.07}|
 ```
 
 Continuous collection over a simple sequence:

docs/language/aggregates/max.md

@@ -18,7 +18,7 @@ echo '1 2 3 4' | zq -z 'max(this)' -
 ```
 =>
 ```mdtest-output
-{max:4}
+4
 ```
 
 Continuous maximum of simple sequence:
@@ -38,5 +38,5 @@ echo '1 2 3 4 "foo"' | zq -z 'max(this)' -
 ```
 =>
 ```mdtest-output
-{max:4}
+4
 ```

docs/language/aggregates/min.md

@@ -18,7 +18,7 @@ echo '1 2 3 4' | zq -z 'min(this)' -
 ```
 =>
 ```mdtest-output
-{min:1}
+1
 ```
 
 Continuous minimum of simple sequence:
@@ -38,5 +38,5 @@ echo '1 2 3 4 "foo"' | zq -z 'min(this)' -
 ```
 =>
 ```mdtest-output
-{min:1}
+1
 ```

docs/language/aggregates/or.md

@@ -18,7 +18,7 @@ echo 'false true false' | zq -z 'or(this)' -
 ```
 =>
 ```mdtest-output
-{or:true}
+true
 ```
 
 Continuous OR of simple sequence:

docs/language/aggregates/sum.md

@@ -18,7 +18,7 @@ echo '1 2 3 4' | zq -z 'sum(this)' -
 ```
 =>
 ```mdtest-output
-{sum:10}
+10
 ```
 
 Continuous sum of simple sequence:
@@ -38,5 +38,5 @@ echo '1 2 3 4 "foo"' | zq -z 'sum(this)' -
 ```
 =>
 ```mdtest-output
-{sum:10}
+10
 ```

docs/language/aggregates/union.md

@@ -21,7 +21,7 @@ echo '1 2 3 3' | zq -z 'union(this)' -
 ```
 =>
 ```mdtest-output
-{union:|[1,2,3]|}
+|[1,2,3]|
 ```
 
 Continuous average of simple sequence:

docs/language/operators/over.md

@@ -115,20 +115,20 @@ echo '{a:[1,2]} {a:[3,4,5]}' | zq -z 'over a | sum(this)' -
 ```
 =>
 ```mdtest-output
-{sum:15}
+15
 ```
 _Aggregate the traversed values in a lateral query_
 ```mdtest-command
 echo '{a:[1,2]} {a:[3,4,5]}' | zq -z 'over a => ( sum(this) )' -
 ```
 =>
 ```mdtest-output
-{sum:3}
-{sum:12}
+3
+12
 ```
 _Access the outer values in a lateral query_
 ```mdtest-command
-echo '{a:[1,2],s:"foo"} {a:[3,4,5],s:"bar"}' | zq -z 'over a with s => (sum(this) | yield {s,sum})' -
+echo '{a:[1,2],s:"foo"} {a:[3,4,5],s:"bar"}' | zq -z 'over a with s => (sum(this) | yield {s,sum:this})' -
 ```
 =>
 ```mdtest-output

docs/language/operators/summarize.md

@@ -30,6 +30,11 @@ A key may be either an expression or a field.  If the key field is omitted,
 it is inferred from the expression, e.g., the field name for `by lower(s)`
 is `lower`.
 
+When the result of `summarize` is a single value (e.g., a single aggregate
+function without group-by keys) and there is no field name specified, then
+the output is that single value rather than a single-field record
+containing that value.
+
 If the cardinality of group-by keys causes the memory footprint to exceed
 a limit, then each aggregate's partial results are spilled to temporary storage
 and the results merged into final results using an external merge sort.
@@ -44,7 +49,27 @@ echo '1 2 3 4' | zq -z 'summarize avg(this)' -
 ```
 =>
 ```mdtest-output
-{avg:2.5}
+2.5
+```
+
+To format the output of a single-valued aggregation into a record, simply specify
+an explicit field for the output:
+```mdtest-command
+echo '1 2 3 4' | zq -z 'summarize mean:=avg(this)' -
+```
+=>
+```mdtest-output
+{mean:2.5}
+```
+
+When multiple aggregate functions are specified, even without explicit field names,
+a record result is generated with field names implied by the functions:
+```mdtest-command
+echo '1 2 3 4' | zq -z 'summarize avg(this),sum(this),count()' -
+```
+=>
+```mdtest-output
+{avg:2.5,sum:10,count:4(uint64)}
 ```
 
 Sum the input sequence, leaving out the `summarize` keyword:
@@ -53,7 +78,7 @@ echo '1 2 3 4' | zq -z 'sum(this)' -
 ```
 =>
 ```mdtest-output
-{sum:10}
+10
 ```
 
 Create integer sets by key and sort the output to get a deterministic order:

docs/language/operators/yield.md

@@ -52,7 +52,7 @@ echo '1 2 3' | zq -z 'yield this*2+1' -
 ```
 _Yield is often used to transform records_
 ```mdtest-command
-echo '{a:1,b:2}{a:3,b:4}' | zq -z 'yield [a,b],[b,a] | collect(this) | yield collect' -
+echo '{a:1,b:2}{a:3,b:4}' | zq -z 'yield [a,b],[b,a] | collect(this)' -
 ```
 =>
 ```mdtest-output