feat(spanner/spansql): add support for aggregate function calls

spanner/spansql/keywords.go

@@ -129,11 +129,16 @@ var keywords = map[string]bool{
 // https://cloud.google.com/spanner/docs/functions-and-operators
 var funcs = make(map[string]bool)
 var funcArgParsers = make(map[string]func(*parser) (Expr, *parseError))
+var aggregateFuncs = make(map[string]bool)
 
 func init() {
-	for _, f := range allFuncs {
+	for _, f := range funcNames {
 		funcs[f] = true
 	}
+	for _, f := range aggregateFuncNames {
+		funcs[f] = true
+		aggregateFuncs[f] = true
+	}
 	// Special case for CAST, SAFE_CAST and EXTRACT
 	funcArgParsers["CAST"] = typedArgParser
 	funcArgParsers["SAFE_CAST"] = typedArgParser
@@ -150,19 +155,9 @@ func init() {
 	funcArgParsers["GET_INTERNAL_SEQUENCE_STATE"] = sequenceArgParser
 }
 
-var allFuncs = []string{
+var funcNames = []string{
 	// TODO: many more
 
-	// Aggregate functions.
-	"ANY_VALUE",
-	"ARRAY_AGG",
-	"AVG",
-	"BIT_XOR",
-	"COUNT",
-	"MAX",
-	"MIN",
-	"SUM",
-
 	// Cast functions.
 	"CAST",
 	"SAFE_CAST",
@@ -295,3 +290,28 @@ var allFuncs = []string{
 	// Utility functions.
 	"GENERATE_UUID",
 }
+
+var aggregateFuncNames = []string{
+	// Aggregate functions.
+	"ANY_VALUE",
+	"ARRAY_AGG",
+	"ARRAY_CONCAT_AGG",
+	"AVG",
+	"BIT_AND",
+	"BIT_OR",
+	"BIT_XOR",
+	"COUNT",
+	"COUNTIF",
+	"LOGICAL_AND",
+	"LOGICAL_OR",
+	"MAX",
+	"MIN",
+	"STRING_AGG",
+	"SUM",
+
+	// Statistical aggregate functions.
+	"STDDEV",
+	"STDDEV_SAMP",
+	"VAR_SAMP",
+	"VARIANCE",
+}

spanner/spansql/parser.go

@@ -3566,6 +3566,65 @@ var sequenceArgParser = func(p *parser) (Expr, *parseError) {
 	return p.parseExpr()
 }
 
+func (p *parser) parseAggregateFunc() (Func, *parseError) {
+	tok := p.next()
+	if tok.err != nil {
+		return Func{}, tok.err
+	}
+	name := strings.ToUpper(tok.value)
+	if err := p.expect("("); err != nil {
+		return Func{}, err
+	}
+	var distinct bool
+	if p.eat("DISTINCT") {
+		distinct = true
+	}
+	args, err := p.parseExprList()
+	if err != nil {
+		return Func{}, err
+	}
+	var nullsHandling NullsHandling
+	if p.eat("IGNORE", "NULLS") {
+		nullsHandling = IgnoreNulls
+	} else if p.eat("RESPECT", "NULLS") {
+		nullsHandling = RespectNulls
+	}
+	var having *AggregateHaving
+	if p.eat("HAVING") {
+		tok := p.next()
+		if tok.err != nil {
+			return Func{}, tok.err
+		}
+		var cond AggregateHavingCondition
+		switch tok.value {
+		case "MAX":
+			cond = HavingMax
+		case "MIN":
+			cond = HavingMin
+		default:
+			return Func{}, p.errorf("got %q, want MAX or MIN", tok.value)
+		}
+		expr, err := p.parseExpr()
+		if err != nil {
+			return Func{}, err
+		}
+		having = &AggregateHaving{
+			Condition: cond,
+			Expr:      expr,
+		}
+	}
+	if err := p.expect(")"); err != nil {
+		return Func{}, err
+	}
+	return Func{
+		Name:          name,
+		Args:          args,
+		Distinct:      distinct,
+		NullsHandling: nullsHandling,
+		Having:        having,
+	}, nil
+}
+
 /*
 Expressions
 
@@ -3918,6 +3977,10 @@ func (p *parser) parseLit() (Expr, *parseError) {
 	// this is a function invocation.
 	// The `funcs` map is keyed by upper case strings.
 	if name := strings.ToUpper(tok.value); funcs[name] && p.sniff("(") {
+		if aggregateFuncs[name] {
+			p.back()
+			return p.parseAggregateFunc()
+		}
 		var list []Expr
 		var err *parseError
 		if f, ok := funcArgParsers[name]; ok {

spanner/spansql/parser_test.go

@@ -419,6 +419,13 @@ func TestParseExpr(t *testing.T) {
 		{`GET_NEXT_SEQUENCE_VALUE(SEQUENCE MySequence)`, Func{Name: "GET_NEXT_SEQUENCE_VALUE", Args: []Expr{SequenceExpr{Name: ID("MySequence")}}}},
 		{`GET_INTERNAL_SEQUENCE_STATE(SEQUENCE MySequence)`, Func{Name: "GET_INTERNAL_SEQUENCE_STATE", Args: []Expr{SequenceExpr{Name: ID("MySequence")}}}},
 
+		// Aggregate Functions
+		{`COUNT(*)`, Func{Name: "COUNT", Args: []Expr{Star}}},
+		{`COUNTIF(DISTINCT cname)`, Func{Name: "COUNTIF", Args: []Expr{ID("cname")}, Distinct: true}},
+		{`ARRAY_AGG(Foo IGNORE NULLS)`, Func{Name: "ARRAY_AGG", Args: []Expr{ID("Foo")}, NullsHandling: IgnoreNulls}},
+		{`ANY_VALUE(Foo HAVING MAX Bar)`, Func{Name: "ANY_VALUE", Args: []Expr{ID("Foo")}, Having: &AggregateHaving{Condition: HavingMax, Expr: ID("Bar")}}},
+		{`STRING_AGG(DISTINCT Foo, "," IGNORE NULLS HAVING MAX Bar)`, Func{Name: "STRING_AGG", Args: []Expr{ID("Foo"), StringLiteral(",")}, Distinct: true, NullsHandling: IgnoreNulls, Having: &AggregateHaving{Condition: HavingMax, Expr: ID("Bar")}}},
+
 		// Conditional expressions
 		{
 			`CASE X WHEN 1 THEN "X" WHEN 2 THEN "Y" ELSE NULL END`,

spanner/spansql/sql.go

@@ -913,7 +913,27 @@ func (f Func) SQL() string { return buildSQL(f) }
 func (f Func) addSQL(sb *strings.Builder) {
 	sb.WriteString(f.Name)
 	sb.WriteString("(")
+	if f.Distinct {
+		sb.WriteString("DISTINCT ")
+	}
 	addExprList(sb, f.Args, ", ")
+	switch f.NullsHandling {
+	case RespectNulls:
+		sb.WriteString(" RESPECT NULLS")
+	case IgnoreNulls:
+		sb.WriteString(" IGNORE NULLS")
+	}
+	if ah := f.Having; ah != nil {
+		sb.WriteString(" HAVING")
+		switch ah.Condition {
+		case HavingMax:
+			sb.WriteString(" MAX")
+		case HavingMin:
+			sb.WriteString(" MIN")
+		}
+		sb.WriteString(" ")
+		sb.WriteString(ah.Expr.SQL())
+	}
 	sb.WriteString(")")
 }
 

spanner/spansql/sql_test.go

@@ -970,6 +970,31 @@ func TestSQL(t *testing.T) {
 			`SELECT SAFE_CAST(7 AS DATE)`,
 			reparseQuery,
 		},
+		{
+			Func{Name: "COUNT", Args: []Expr{Star}},
+			`COUNT(*)`,
+			reparseExpr,
+		},
+		{
+			Func{Name: "COUNTIF", Args: []Expr{ID("cname")}, Distinct: true},
+			`COUNTIF(DISTINCT cname)`,
+			reparseExpr,
+		},
+		{
+			Func{Name: "ARRAY_AGG", Args: []Expr{ID("Foo")}, NullsHandling: IgnoreNulls},
+			`ARRAY_AGG(Foo IGNORE NULLS)`,
+			reparseExpr,
+		},
+		{
+			Func{Name: "ANY_VALUE", Args: []Expr{ID("Foo")}, Having: &AggregateHaving{Condition: HavingMax, Expr: ID("Bar")}},
+			`ANY_VALUE(Foo HAVING MAX Bar)`,
+			reparseExpr,
+		},
+		{
+			Func{Name: "STRING_AGG", Args: []Expr{ID("Foo"), StringLiteral(",")}, Distinct: true, NullsHandling: IgnoreNulls, Having: &AggregateHaving{Condition: HavingMax, Expr: ID("Bar")}},
+			`STRING_AGG(DISTINCT Foo, "," IGNORE NULLS HAVING MAX Bar)`,
+			reparseExpr,
+		},
 		{
 			ComparisonOp{LHS: ID("X"), Op: NotBetween, RHS: ID("Y"), RHS2: ID("Z")},
 			`X NOT BETWEEN Y AND Z`,

spanner/spansql/types.go

@@ -757,7 +757,9 @@ type Func struct {
 	Name string // not ID
 	Args []Expr
 
-	// TODO: various functions permit as-expressions, which might warrant different types in here.
+	Distinct      bool
+	NullsHandling NullsHandling
+	Having        *AggregateHaving
 }
 
 func (Func) isBoolExpr() {} // possibly bool
@@ -804,6 +806,29 @@ type SequenceExpr struct {
 
 func (SequenceExpr) isExpr() {}
 
+// NullsHandling represents the method of dealing with NULL values in aggregate functions.
+type NullsHandling int
+
+const (
+	NullsHandlingUnspecified NullsHandling = iota
+	RespectNulls
+	IgnoreNulls
+)
+
+// AggregateHaving represents the HAVING clause specific to aggregate functions, restricting rows based on a maximal or minimal value.
+type AggregateHaving struct {
+	Condition AggregateHavingCondition
+	Expr      Expr
+}
+
+// AggregateHavingCondition represents the condition (MAX or MIN) for the AggregateHaving clause.
+type AggregateHavingCondition int
+
+const (
+	HavingMax AggregateHavingCondition = iota
+	HavingMin
+)
+
 // Paren represents a parenthesised expression.
 type Paren struct {
 	Expr Expr