Gen4: Distinct

go/mysql/sql_error.go

@@ -191,6 +191,7 @@ var stateToMysqlCode = map[vterrors.State]struct {
 	vterrors.WrongNumberOfColumnsInSelect: {num: ERWrongNumberOfColumnsInSelect, state: SSWrongNumberOfColumns},
 	vterrors.WrongTypeForVar:              {num: ERWrongTypeForVar, state: SSClientError},
 	vterrors.WrongValueForVar:             {num: ERWrongValueForVar, state: SSClientError},
+	vterrors.WrongFieldWithGroup:          {num: ERWrongFieldWithGroup, state: SSClientError},
 	vterrors.ServerNotAvailable:           {num: ERServerIsntAvailable, state: SSNetError},
 	vterrors.CantDoThisInTransaction:      {num: ERCantDoThisDuringAnTransaction, state: SSCantDoThisDuringAnTransaction},
 	vterrors.RequiresPrimaryKey:           {num: ERRequiresPrimaryKey, state: SSClientError},

go/vt/sqlparser/ast_funcs.go

@@ -1371,17 +1371,22 @@ func ToString(exprs []TableExpr) string {
 func ContainsAggregation(e Expr) bool {
 	hasAggregates := false
 	_ = Walk(func(node SQLNode) (kontinue bool, err error) {
-		switch node := node.(type) {
-		case *FuncExpr:
-			if node.IsAggregate() {
-				hasAggregates = true
-				return false, nil
-			}
-		case *GroupConcatExpr:
+		if IsAggregation(node) {
 			hasAggregates = true
 			return false, nil
 		}
 		return true, nil
 	}, e)
 	return hasAggregates
 }
+
+// IsAggregation returns true if the node is an aggregation expression
+func IsAggregation(node SQLNode) bool {
+	switch node := node.(type) {
+	case *FuncExpr:
+		return node.IsAggregate()
+	case *GroupConcatExpr:
+		return true
+	}
+	return false
+}

go/vt/vterrors/state.go

@@ -35,6 +35,7 @@ const (
 	NonUniqTable
 	NonUpdateableTable
 	SyntaxError
+	WrongFieldWithGroup
 	WrongGroupField
 	WrongTypeForVar
 	WrongValueForVar

go/vt/vtgate/planbuilder/abstract/queryprojection.go

@@ -38,6 +38,7 @@ type (
 		// If you change the contents here, please update the toString() method
 		SelectExprs        []SelectExpr
 		HasAggr            bool
+		Distinct           bool
 		GroupByExprs       []GroupBy
 		OrderExprs         []OrderBy
 		CanPushDownSorting bool
@@ -58,39 +59,28 @@ type (
 
 // CreateQPFromSelect created the QueryProjection for the input *sqlparser.Select
 func CreateQPFromSelect(sel *sqlparser.Select) (*QueryProjection, error) {
-	qp := &QueryProjection{}
+	qp := &QueryProjection{
+		Distinct: sel.Distinct,
+	}
 
-	hasNonAggr := false
 	for _, selExp := range sel.SelectExprs {
 		exp, ok := selExp.(*sqlparser.AliasedExpr)
 		if !ok {
 			return nil, semantics.Gen4NotSupportedF("%T in select list", selExp)
 		}
-		fExpr, ok := exp.Expr.(*sqlparser.FuncExpr)
-		if ok && fExpr.IsAggregate() {
-			if len(fExpr.Exprs) != 1 {
-				return nil, vterrors.NewErrorf(vtrpcpb.Code_INVALID_ARGUMENT, vterrors.SyntaxError, "aggregate functions take a single argument '%s'", sqlparser.String(fExpr))
-			}
-			if fExpr.Distinct {
-				return nil, semantics.Gen4NotSupportedF("distinct aggregation")
-			}
-			qp.HasAggr = true
-			qp.SelectExprs = append(qp.SelectExprs, SelectExpr{
-				Col:  exp,
-				Aggr: true,
-			})
-			continue
-		}
 
+		if err := checkForInvalidAggregations(exp); err != nil {
+			return nil, err
+		}
+		col := SelectExpr{
+			Col: exp,
+		}
 		if sqlparser.ContainsAggregation(exp.Expr) {
-			return nil, vterrors.New(vtrpcpb.Code_UNIMPLEMENTED, "unsupported: in scatter query: complex aggregate expression")
+			col.Aggr = true
+			qp.HasAggr = true
 		}
-		hasNonAggr = true
-		qp.SelectExprs = append(qp.SelectExprs, SelectExpr{Col: exp})
-	}
 
-	if hasNonAggr && qp.HasAggr && sel.GroupBy == nil {
-		return nil, vterrors.NewErrorf(vtrpcpb.Code_INVALID_ARGUMENT, vterrors.MixOfGroupFuncAndFields, "Mixing of aggregation and non-aggregation columns is not allowed if there is no GROUP BY clause")
+		qp.SelectExprs = append(qp.SelectExprs, col)
 	}
 
 	for _, group := range sel.GroupBy {
@@ -104,6 +94,18 @@ func CreateQPFromSelect(sel *sqlparser.Select) (*QueryProjection, error) {
 		qp.GroupByExprs = append(qp.GroupByExprs, GroupBy{Inner: expr, WeightStrExpr: weightStrExpr})
 	}
 
+	if qp.HasAggr {
+		expr := qp.getNonAggrExprNotMatchingGroupByExprs()
+		// if we have aggregation functions, non aggregating columns and GROUP BY,
+		// the non-aggregating expressions must all be listed in the GROUP BY list
+		if expr != nil {
+			if len(qp.GroupByExprs) > 0 {
+				return nil, vterrors.NewErrorf(vtrpcpb.Code_INVALID_ARGUMENT, vterrors.WrongFieldWithGroup, "Expression of SELECT list is not in GROUP BY clause and contains nonaggregated column '%s' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by", sqlparser.String(expr))
+			}
+			return nil, vterrors.NewErrorf(vtrpcpb.Code_INVALID_ARGUMENT, vterrors.MixOfGroupFuncAndFields, "In aggregated query without GROUP BY, expression of SELECT list contains nonaggregated column '%s'; this is incompatible with sql_mode=only_full_group_by", sqlparser.String(expr))
+		}
+	}
+
 	canPushDownSorting := true
 	for _, order := range sel.OrderBy {
 		expr, weightStrExpr, err := qp.getSimplifiedExpr(order.Expr, "order clause")
@@ -119,11 +121,47 @@ func CreateQPFromSelect(sel *sqlparser.Select) (*QueryProjection, error) {
 		})
 		canPushDownSorting = canPushDownSorting && !sqlparser.ContainsAggregation(weightStrExpr)
 	}
+	if qp.Distinct && !qp.HasAggr {
+		qp.GroupByExprs = nil
+	}
 	qp.CanPushDownSorting = canPushDownSorting
-
 	return qp, nil
 }
 
+func checkForInvalidAggregations(exp *sqlparser.AliasedExpr) error {
+	return sqlparser.Walk(func(node sqlparser.SQLNode) (kontinue bool, err error) {
+		fExpr, ok := node.(*sqlparser.FuncExpr)
+		if ok && fExpr.IsAggregate() {
+			if len(fExpr.Exprs) != 1 {
+				return false, vterrors.NewErrorf(vtrpcpb.Code_INVALID_ARGUMENT, vterrors.SyntaxError, "aggregate functions take a single argument '%s'", sqlparser.String(fExpr))
+			}
+			if fExpr.Distinct {
+				return false, semantics.Gen4NotSupportedF("distinct aggregation")
+			}
+		}
+		return true, nil
+	}, exp.Expr)
+}
+
+func (qp *QueryProjection) getNonAggrExprNotMatchingGroupByExprs() sqlparser.Expr {
+	for _, expr := range qp.SelectExprs {
+		if expr.Aggr {
+			continue
+		}
+		isGroupByOk := false
+		for _, groupByExpr := range qp.GroupByExprs {
+			if sqlparser.EqualsExpr(groupByExpr.WeightStrExpr, expr.Col.Expr) {
+				isGroupByOk = true
+				break
+			}
+		}
+		if !isGroupByOk {
+			return expr.Col.Expr
+		}
+	}
+	return nil
+}
+
 // getSimplifiedExpr takes an expression used in ORDER BY or GROUP BY, which can reference both aliased columns and
 // column offsets, and returns an expression that is simpler to evaluate
 func (qp *QueryProjection) getSimplifiedExpr(e sqlparser.Expr, caller string) (expr sqlparser.Expr, weightStrExpr sqlparser.Expr, err error) {
@@ -169,11 +207,13 @@ func (qp *QueryProjection) toString() string {
 		Select   []string
 		Grouping []string
 		OrderBy  []string
+		Distinct bool
 	}
 	out := output{
 		Select:   []string{},
 		Grouping: []string{},
 		OrderBy:  []string{},
+		Distinct: qp.NeedsDistinct(),
 	}
 
 	for _, expr := range qp.SelectExprs {
@@ -204,3 +244,26 @@ func (qp *QueryProjection) toString() string {
 func (qp *QueryProjection) NeedsAggregation() bool {
 	return qp.HasAggr || len(qp.GroupByExprs) > 0
 }
+
+func (qp QueryProjection) onlyAggr() bool {
+	if !qp.HasAggr {
+		return false
+	}
+	for _, expr := range qp.SelectExprs {
+		if !expr.Aggr {
+			return false
+		}
+	}
+	return true
+}
+
+// NeedsDistinct returns true if the query needs explicit distinct
+func (qp *QueryProjection) NeedsDistinct() bool {
+	if !qp.Distinct {
+		return false
+	}
+	if qp.onlyAggr() && len(qp.GroupByExprs) == 0 {
+		return false
+	}
+	return true
+}

go/vt/vtgate/planbuilder/abstract/queryprojection_test.go

@@ -46,7 +46,7 @@ func TestQP(t *testing.T) {
 		},
 		{
 			sql:    "select 1, count(1) from user",
-			expErr: "Mixing of aggregation and non-aggregation columns is not allowed if there is no GROUP BY clause",
+			expErr: "In aggregated query without GROUP BY, expression of SELECT list contains nonaggregated column '1'; this is incompatible with sql_mode=only_full_group_by",
 		},
 		{
 			sql: "select max(id) from user",
@@ -55,13 +55,9 @@ func TestQP(t *testing.T) {
 			sql:    "select max(a, b) from user",
 			expErr: "aggregate functions take a single argument 'max(a, b)'",
 		},
-		{
-			sql:    "select func(max(id)) from user",
-			expErr: "unsupported: in scatter query: complex aggregate expression",
-		},
 		{
 			sql:    "select 1, count(1) from user order by 1",
-			expErr: "Mixing of aggregation and non-aggregation columns is not allowed if there is no GROUP BY clause",
+			expErr: "In aggregated query without GROUP BY, expression of SELECT list contains nonaggregated column '1'; this is incompatible with sql_mode=only_full_group_by",
 		},
 		{
 			sql: "select id from user order by col, id, 1",
@@ -132,7 +128,8 @@ func TestQPSimplifiedExpr(t *testing.T) {
   "Grouping": [
     "intcol"
   ],
-  "OrderBy": []
+  "OrderBy": [],
+  "Distinct": false
 }`,
 		},
 		{
@@ -147,7 +144,8 @@ func TestQPSimplifiedExpr(t *testing.T) {
   "OrderBy": [
     "intcol asc",
     "textcol asc"
-  ]
+  ],
+  "Distinct": false
 }`,
 		},
 		{
@@ -166,7 +164,33 @@ func TestQPSimplifiedExpr(t *testing.T) {
   ],
   "OrderBy": [
     "textcol desc"
-  ]
+  ],
+  "Distinct": false
+}`,
+		},
+		{
+			query: "select distinct col1, col2 from user group by col1, col2",
+			expected: `
+{
+  "Select": [
+    "col1",
+    "col2"
+  ],
+  "Grouping": [],
+  "OrderBy": [],
+  "Distinct": true
+}`,
+		},
+		{
+			query: "select distinct count(*) from user",
+			expected: `
+{
+  "Select": [
+    "aggr: count(*)"
+  ],
+  "Grouping": [],
+  "OrderBy": [],
+  "Distinct": false
 }`,
 		},
 	}

go/vt/vtgate/planbuilder/distinct.go

@@ -24,11 +24,7 @@ import (
 
 var _ logicalPlan = (*distinct)(nil)
 
-// limit is the logicalPlan for engine.Limit.
-// This gets built if a limit needs to be applied
-// after rows are returned from an underlying
-// operation. Since a limit is the final operation
-// of a SELECT, most pushes are not applicable.
+// distinct is the logicalPlan for engine.Distinct.
 type distinct struct {
 	logicalPlanCommon
 }