Add the EXISTS Operator for Select Where Filters (#572)

EXISTS expression and where filter

enginetest/memory_engine_test.go

@@ -124,30 +124,35 @@ func TestSingleScript(t *testing.T) {
 		{
 			Name: "Issue #499",
 			SetUpScript: []string{
-				"CREATE TABLE test (time TIMESTAMP, value DOUBLE);",
-				`INSERT INTO test VALUES 
-			("2021-07-04 10:00:00", 1.0),
-			("2021-07-03 10:00:00", 2.0),
-			("2021-07-02 10:00:00", 3.0),
-			("2021-07-01 10:00:00", 4.0);`,
+				"CREATE TABLE test (pk int primary key);",
+				`INSERT INTO test values (1),(2);`,
+				`CREATE TABLE t2 (pk int)`,
+				`INSERT INTO t2 VALUES (NULL)`,
 			},
 			Assertions: []enginetest.ScriptTestAssertion{
 				{
-					Query: `SELECT
-				UNIX_TIMESTAMP(time) DIV 60 * 60 AS "time",
-				avg(value) AS "value"
-    			FROM test
-    			GROUP BY 1
-    			ORDER BY UNIX_TIMESTAMP(time) DIV 60 * 60`,
+					Query: `SELECT * FROM test WHERE EXISTS (SELECT pk FROM t2)`,
 					Expected: []sql.Row{
-						{1625133600, 4.0},
-						{1625220000, 3.0},
-						{1625306400, 2.0},
-						{1625392800, 1.0},
+						{1},
+						{2},
 					},
 				},
 			},
 		},
+		{
+			Name: "Issue #499",
+			SetUpScript: []string{
+				"CREATE TABLE test2 (pk int primary key);",
+				`INSERT INTO test2 values (1),(2);`,
+				`CREATE TABLE t2 (pk int)`,
+			},
+			Assertions: []enginetest.ScriptTestAssertion{
+				{
+					Query:    `SELECT * FROM test2 WHERE EXISTS (SELECT pk FROM t2)`,
+					Expected: []sql.Row{},
+				},
+			},
+		},
 	}
 
 	for _, test := range scripts {

enginetest/queries.go

@@ -5284,6 +5284,50 @@ var QueryTests = []QueryTest{
 			{time.Date(2020, 1, 1, 16, 0, 0, 0, time.UTC)},
 		},
 	},
+	{
+		Query: `SELECT 1 from dual WHERE EXISTS (SELECT 1 from dual);`,
+		Expected: []sql.Row{
+			{1},
+		},
+	},
+	{
+		Query: `SELECT 1 from dual WHERE EXISTS (SELECT NULL from dual);`,
+		Expected: []sql.Row{
+			{1},
+		},
+	},
+	{
+		Query:    `SELECT * FROM two_pk WHERE EXISTS (SELECT pk FROM one_pk WHERE pk > 4)`,
+		Expected: []sql.Row{},
+	},
+	{
+		Query:    `SELECT 2 + 2 WHERE NOT EXISTS (SELECT pk FROM one_pk WHERE pk > 4)`,
+		Expected: []sql.Row{{4}},
+	},
+	{
+		Query:    `SELECT distinct pk1 FROM two_pk WHERE EXISTS (SELECT pk from one_pk where pk <= two_pk.pk1)`,
+		Expected: []sql.Row{{0}, {1}},
+	},
+	{
+		Query:    `select pk from one_pk where exists (SELECT pk1 FROM two_pk);`,
+		Expected: []sql.Row{{0}, {1}, {2}, {3}},
+	},
+	{
+		Query:    `SELECT EXISTS (SELECT NULL from dual);`,
+		Expected: []sql.Row{{true}},
+	},
+	{
+		Query:    `SELECT NOT EXISTS (SELECT NULL FROM dual)`,
+		Expected: []sql.Row{{false}},
+	},
+	{
+		Query:    `select exists (SELECT pk1 FROM two_pk);`,
+		Expected: []sql.Row{{true}},
+	},
+	{
+		Query:    `SELECT EXISTS (SELECT pk FROM one_pk WHERE pk > 4)`,
+		Expected: []sql.Row{{false}},
+	},
 }
 
 var KeylessQueries = []QueryTest{
@@ -6471,6 +6515,10 @@ var errorQueries = []QueryErrorTest{
 		Query:       "select ((4,5),((1,2),3)) = ((1,2),(4,5)) from dual",
 		ExpectedErr: sql.ErrInvalidOperandColumns,
 	},
+	{
+		Query:       "SELECT (2, 2)=1 FROM dual where exists (SELECT 1 FROM dual)",
+		ExpectedErr: sql.ErrInvalidOperandColumns,
+	},
 }
 
 // WriteQueryTest is a query test for INSERT, UPDATE, etc. statements. It has a query to run and a select query to

enginetest/script_queries.go

@@ -1170,6 +1170,21 @@ var ScriptTests = []ScriptTest{
 			},
 		},
 	},
+	{
+		Name: "Slightly more complex example for the Exists Clause",
+		SetUpScript: []string{
+			"create table store(store_id int, item_id int, primary key (store_id, item_id))",
+			"create table items(item_id int primary key, price int)",
+			"insert into store values (0, 1), (0,2),(0,3),(1,2),(1,4),(2,1)",
+			"insert into items values (1, 10), (2, 20), (3, 30),(4,40)",
+		},
+		Assertions: []ScriptTestAssertion{
+			{
+				Query:    "SELECT * from store WHERE EXISTS (SELECT price from items where price > 10 and store.item_id = items.item_id)",
+				Expected: []sql.Row{{0, 2}, {0, 3}, {1, 2}, {1, 4}},
+			},
+		},
+	},
 }
 
 var CreateCheckConstraintsScripts = []ScriptTest{

sql/parse/parse.go

@@ -2436,6 +2436,13 @@ func ExprToExpression(ctx *sql.Context, e sqlparser.Expr) (sql.Expression, error
 			return nil, err
 		}
 		return expression.NewUnresolvedFunction("values", false, nil, col), nil
+	case *sqlparser.ExistsExpr:
+		subqueryExp, err := ExprToExpression(ctx, v.Subquery)
+		if err != nil {
+			return nil, err
+		}
+
+		return plan.NewExistsSubquery(subqueryExp), nil
 	}
 }
 

sql/plan/existssubquery.go

@@ -0,0 +1,85 @@
+// Copyright 2020-2021 Dolthub, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package plan
+
+import (
+	"fmt"
+
+	"github.com/dolthub/go-mysql-server/sql"
+	"github.com/dolthub/go-mysql-server/sql/expression"
+)
+
+// ExistsSubquery is an expression that checks that a subquery returns a non-empty result set. It's in the plan package,
+// instead of the expression package, because Subquery is itself in the plan package (because it functions more like a
+// plan node than an expression in its evaluation).
+type ExistsSubquery struct {
+	subquery expression.UnaryExpression
+}
+
+var _ sql.Expression = (*ExistsSubquery)(nil)
+
+//NewExistsSubquery created an ExistsSubquery expression.
+func NewExistsSubquery(query sql.Expression) *ExistsSubquery {
+	return &ExistsSubquery{expression.UnaryExpression{Child: query}}
+}
+
+// Eval implements the Expression interface.
+func (e *ExistsSubquery) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
+	subquery, ok := e.subquery.Child.(*Subquery)
+	if !ok {
+		return nil, fmt.Errorf("error: exists operator should only work with a subquery")
+	}
+
+	hasResultRow, err := subquery.HasResultRow(ctx, row)
+	if err != nil {
+		return nil, err
+	}
+
+	return hasResultRow, nil
+}
+
+// WithChildren implements the Expression interface.
+func (e *ExistsSubquery) WithChildren(children ...sql.Expression) (sql.Expression, error) {
+	if len(children) != 1 {
+		return nil, sql.ErrInvalidChildrenNumber.New(e, len(children), 1)
+	}
+
+	return NewExistsSubquery(children[0]), nil
+}
+
+// Resolved implements the Expression interface.
+func (e *ExistsSubquery) Resolved() bool {
+	return e.subquery.Resolved()
+}
+
+// IsNullable implements the Expression interface.
+func (e *ExistsSubquery) IsNullable() bool {
+	return false
+}
+
+// Children implements the Expression interface.
+func (e *ExistsSubquery) Children() []sql.Expression {
+	return []sql.Expression{e.subquery.Child}
+}
+
+// String implements the Expression interface.
+func (e *ExistsSubquery) String() string {
+	return fmt.Sprintf("EXISTS %s", e.subquery)
+}
+
+// Type implements the Expression interface.
+func (e *ExistsSubquery) Type() sql.Type {
+	return sql.Boolean
+}

sql/plan/existssubquery_test.go

@@ -0,0 +1,99 @@
+// Copyright 2020-2021 Dolthub, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package plan_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/dolthub/go-mysql-server/memory"
+	"github.com/dolthub/go-mysql-server/sql"
+	"github.com/dolthub/go-mysql-server/sql/expression"
+	"github.com/dolthub/go-mysql-server/sql/plan"
+)
+
+func TestExistsSubquery(t *testing.T) {
+	ctx := sql.NewEmptyContext()
+	table := memory.NewTable("foo", sql.Schema{
+		{Name: "t", Source: "foo", Type: sql.Text},
+	})
+
+	require.NoError(t, table.Insert(ctx, sql.Row{"one"}))
+	require.NoError(t, table.Insert(ctx, sql.Row{"two"}))
+	require.NoError(t, table.Insert(ctx, sql.Row{"three"}))
+
+	emptyTable := memory.NewTable("empty", sql.Schema{
+		{Name: "t", Source: "empty", Type: sql.Int64},
+	})
+
+	project := func(expr sql.Expression, tbl *memory.Table) sql.Node {
+		return plan.NewProject([]sql.Expression{
+			expr,
+		}, plan.NewResolvedTable(tbl, nil, nil))
+	}
+
+	testCases := []struct {
+		name     string
+		subquery sql.Node
+		row      sql.Row
+		result   interface{}
+	}{
+		{
+			"Null returns as true",
+			project(
+				expression.NewGetField(1, sql.Text, "foo", false), table,
+			),
+			sql.NewRow(nil),
+			true,
+		},
+		{
+			"Non NULL evaluates as true",
+			project(
+				expression.NewGetField(1, sql.Text, "foo", false), table,
+			),
+			sql.NewRow("four"),
+			true,
+		},
+		{
+			"Empty Set Passes",
+			project(
+				expression.NewGetField(1, sql.Text, "foo", false), emptyTable,
+			),
+			sql.NewRow(),
+			false,
+		},
+	}
+
+	for _, tt := range testCases {
+		t.Run(tt.name, func(t *testing.T) {
+			require := require.New(t)
+
+			result, err := plan.NewExistsSubquery(
+				plan.NewSubquery(tt.subquery, ""),
+			).Eval(sql.NewEmptyContext(), tt.row)
+			require.NoError(err)
+			require.Equal(tt.result, result)
+
+			// Test Not Exists
+			result, err = expression.NewNot(plan.NewExistsSubquery(
+				plan.NewSubquery(tt.subquery, ""),
+			)).Eval(sql.NewEmptyContext(), tt.row)
+
+			require.NoError(err)
+			require.Equal(tt.result, !result.(bool))
+		})
+	}
+}

sql/plan/subquery.go

@@ -316,6 +316,47 @@ func (s *Subquery) HashMultiple(ctx *sql.Context, row sql.Row) (sql.KeyValueCach
 	return cache, putAllRows(cache, result)
 }
 
+// HasResultRow returns whether the subquery has a result set > 0.
+func (s *Subquery) HasResultRow(ctx *sql.Context, row sql.Row) (bool, error) {
+	// First check if the query was cached.
+	s.cacheMu.Lock()
+	cached := s.resultsCached
+	s.cacheMu.Unlock()
+
+	if cached {
+		return len(s.cache) > 0, nil
+	}
+
+	// Any source of rows, as well as any node that alters the schema of its children, needs to be wrapped so that its
+	// result rows are prepended with the scope row.
+	q, err := TransformUp(s.Query, prependRowInPlan(row))
+	if err != nil {
+		return false, err
+	}
+
+	iter, err := q.RowIter(ctx, row)
+	if err != nil {
+		return false, err
+	}
+
+	// Call the iterator once and see if it has a row. If io.EOF is received return false.
+	_, err = iter.Next()
+	if err == io.EOF {
+		return false, nil
+	}
+
+	if err != nil {
+		return false, err
+	}
+
+	err = iter.Close(ctx)
+	if err != nil {
+		return false, err
+	}
+
+	return true, nil
+}
+
 func putAllRows(cache sql.KeyValueCache, vals []interface{}) error {
 	for _, val := range vals {
 		rowKey, err := sql.HashOf(sql.NewRow(val))