planner: reimplement DEFAULT function to make the behavior consistent…

… with MySQL when looking up the corresponding column (#19709)

expression/simple_rewriter.go

@@ -178,7 +178,7 @@ func FindFieldName(names types.NameSlice, astCol *ast.ColumnName) (int, error) {
 			if idx == -1 {
 				idx = i
 			} else {
-				return -1, errNonUniq.GenWithStackByArgs(name.String(), "field list")
+				return -1, errNonUniq.GenWithStackByArgs(astCol.String(), "field list")
 			}
 		}
 	}

go.mod

@@ -37,7 +37,7 @@ require (
 	github.com/pingcap/goleveldb v0.0.0-20191226122134-f82aafb29989
 	github.com/pingcap/kvproto v0.0.0-20200828054126-d677e6fd224a
 	github.com/pingcap/log v0.0.0-20200828042413-fce0951f1463
-	github.com/pingcap/parser v0.0.0-20200916082702-907ee5aa5a1c
+	github.com/pingcap/parser v0.0.0-20200918092742-715be3ca6376
 	github.com/pingcap/sysutil v0.0.0-20200715082929-4c47bcac246a
 	github.com/pingcap/tidb-tools v4.0.5-0.20200820092506-34ea90c93237+incompatible
 	github.com/pingcap/tipb v0.0.0-20200618092958-4fad48b4c8c3

go.sum

@@ -509,8 +509,9 @@ github.com/pingcap/parser v0.0.0-20200609110328-c65941b9fbb3/go.mod h1:vQdbJqobJ
 github.com/pingcap/parser v0.0.0-20200623082809-b74301ac298b/go.mod h1:vQdbJqobJAgFyiRNNtXahpMoGWwPEuWciVEK5A20NS0=
 github.com/pingcap/parser v0.0.0-20200730092557-34a468e9b774/go.mod h1:vQdbJqobJAgFyiRNNtXahpMoGWwPEuWciVEK5A20NS0=
 github.com/pingcap/parser v0.0.0-20200731033026-84f62115187c/go.mod h1:vQdbJqobJAgFyiRNNtXahpMoGWwPEuWciVEK5A20NS0=
-github.com/pingcap/parser v0.0.0-20200916082702-907ee5aa5a1c h1:23Lax6TMhmr/DFQCIjGqyJaTSXM/HKMzXcp2L0gVzxY=
-github.com/pingcap/parser v0.0.0-20200916082702-907ee5aa5a1c/go.mod h1:RlLfMRJwFBSiXd2lUaWdV5pSXtrpyvZM8k5bbZWsheU=
+github.com/pingcap/parser v0.0.0-20200813083329-a4bff035d3e2/go.mod h1:vQdbJqobJAgFyiRNNtXahpMoGWwPEuWciVEK5A20NS0=
+github.com/pingcap/parser v0.0.0-20200918092742-715be3ca6376 h1:0j5pdKdpPj2g4UiNVKXkc5qBv6Ci57fymWIChAV2ZVk=
+github.com/pingcap/parser v0.0.0-20200918092742-715be3ca6376/go.mod h1:RlLfMRJwFBSiXd2lUaWdV5pSXtrpyvZM8k5bbZWsheU=
 github.com/pingcap/pd/v4 v4.0.0-rc.1.0.20200422143320-428acd53eba2/go.mod h1:s+utZtXDznOiL24VK0qGmtoHjjXNsscJx3m1n8cC56s=
 github.com/pingcap/pd/v4 v4.0.0-rc.2.0.20200520083007-2c251bd8f181/go.mod h1:q4HTx/bA8aKBa4S7L+SQKHvjRPXCRV0tA0yRw0qkZSA=
 github.com/pingcap/pd/v4 v4.0.0-rc.2.0.20200714122454-1a64f969cb3c/go.mod h1:v/dY4mVkt3dh/Liphhk0E4ScOkZpIk0m0GvWJ9FapDs=

planner/core/expression_rewriter.go

@@ -1655,25 +1655,38 @@ func (er *expressionRewriter) toColumn(v *ast.ColumnName) {
 }
 
 func (er *expressionRewriter) evalDefaultExpr(v *ast.DefaultExpr) {
-	stkLen := len(er.ctxStack)
-	name := er.ctxNameStk[stkLen-1]
-	switch er.ctxStack[stkLen-1].(type) {
-	case *expression.Column:
-	case *expression.CorrelatedColumn:
-	default:
-		idx, err := expression.FindFieldName(er.names, v.Name)
+	var name *types.FieldName
+	// Here we will find the corresponding column for default function. At the same time, we need to consider the issue
+	// of subquery and name space.
+	// For example, we have two tables t1(a int default 1, b int) and t2(a int default -1, c int). Consider the following SQL:
+	// 		select a from t1 where a > (select default(a) from t2)
+	// Refer to the behavior of MySQL, we need to find column a in table t2. If table t2 does not have column a, then find it
+	// in table t1. If there are none, return an error message.
+	// Based on the above description, we need to look in er.b.allNames from back to front.
+	for i := len(er.b.allNames) - 1; i >= 0; i-- {
+		idx, err := expression.FindFieldName(er.b.allNames[i], v.Name)
 		if err != nil {
 			er.err = err
 			return
 		}
-		if er.err != nil {
+		if idx >= 0 {
+			name = er.b.allNames[i][idx]
+			break
+		}
+	}
+	if name == nil {
+		idx, err := expression.FindFieldName(er.names, v.Name)
+		if err != nil {
+			er.err = err
 			return
 		}
 		if idx < 0 {
-			er.err = ErrUnknownColumn.GenWithStackByArgs(v.Name.OrigColName(), "field_list")
+			er.err = ErrUnknownColumn.GenWithStackByArgs(v.Name.OrigColName(), "field list")
 			return
 		}
+		name = er.names[idx]
 	}
+
 	dbName := name.DBName
 	if dbName.O == "" {
 		// if database name is not specified, use current database name
@@ -1721,7 +1734,6 @@ func (er *expressionRewriter) evalDefaultExpr(v *ast.DefaultExpr) {
 	if er.err != nil {
 		return
 	}
-	er.ctxStackPop(1)
 	er.ctxStackAppend(val, types.EmptyName)
 }
 

planner/core/expression_rewriter_test.go

@@ -99,7 +99,7 @@ func (s *testExpressionRewriterSuite) TestDefaultFunction(c *C) {
 	tk.MustExec("create table t2(a varchar(10), b varchar(10))")
 	tk.MustExec("insert into t2 values ('1', '1')")
 	err = tk.ExecToErr("select default(a) from t1, t2")
-	c.Assert(err.Error(), Equals, "[planner:1052]Column 'a' in field list is ambiguous")
+	c.Assert(err.Error(), Equals, "[expression:1052]Column 'a' in field list is ambiguous")
 	tk.MustQuery("select default(t1.a) from t1, t2").Check(testkit.Rows("def"))
 
 	tk.MustExec(`create table t3(
@@ -130,6 +130,21 @@ func (s *testExpressionRewriterSuite) TestDefaultFunction(c *C) {
 
 	tk.MustExec("update t1 set c = c + default(c)")
 	tk.MustQuery("select c from t1").Check(testkit.Rows("11"))
+
+	tk.MustExec("create table t6(a int default -1, b int)")
+	tk.MustExec(`insert into t6 values (0, 0), (1, 1), (2, 2)`)
+	tk.MustExec("create table t7(a int default 1, b int)")
+	tk.MustExec(`insert into t7 values (0, 0), (1, 1), (2, 2)`)
+
+	tk.MustQuery(`select a from t6 where a > (select default(a) from t7 where t6.a = t7.a)`).Check(testkit.Rows("2"))
+	tk.MustQuery(`select a, default(a) from t6 where a > (select default(a) from t7 where t6.a = t7.a)`).Check(testkit.Rows("2 -1"))
+
+	tk.MustExec("create table t8(a int default 1, b int default -1)")
+	tk.MustExec(`insert into t8 values (0, 0), (1, 1)`)
+
+	tk.MustQuery(`select a, a from t8 order by default(a)`).Check(testkit.Rows("0 0", "1 1"))
+	tk.MustQuery(`select a from t8 order by default(b)`).Check(testkit.Rows("0", "1"))
+	tk.MustQuery(`select a from t8 order by default(b) * a`).Check(testkit.Rows("1", "0"))
 }
 
 func (s *testExpressionRewriterSuite) TestCompareSubquery(c *C) {

planner/core/logical_plan_builder.go

@@ -2669,6 +2669,15 @@ func (b *PlanBuilder) buildSelect(ctx context.Context, sel *ast.SelectStmt) (p L
 		return nil, err
 	}
 
+	// b.allNames will be used in evalDefaultExpr(). Default function is special because it needs to find the
+	// corresponding column name, but does not need the value in the column.
+	// For example, select a from t order by default(b), the column b will not be in select fields. Also because
+	// buildSort is after buildProjection, so we need get OutputNames before BuildProjection and store in allNames.
+	// Otherwise, we will get select fields instead of all OutputNames, so that we can't find the column b in the
+	// above example.
+	b.allNames = append(b.allNames, p.OutputNames())
+	defer func() { b.allNames = b.allNames[:len(b.allNames)-1] }()
+
 	if sel.Where != nil {
 		p, err = b.buildSelection(ctx, p, sel.Where, nil)
 		if err != nil {

planner/core/planbuilder.go

@@ -445,6 +445,10 @@ type PlanBuilder struct {
 	partitionedTable []table.PartitionedTable
 	// CreateView needs this information to check whether exists nested view.
 	underlyingViewNames set.StringSet
+
+	// evalDefaultExpr needs this information to find the corresponding column.
+	// It stores the OutputNames before buildProjection.
+	allNames [][]*types.FieldName
 }
 
 type handleColHelper struct {