expression: avoid unnecessary warnings/errors when folding constants …

…in control expr (#19675)

* reduce unnecessary warnings/errors in constrant fold

* update formate

* add commits

Co-authored-by: Yuanjia Zhang <zhangyuanjia@pingcap.com>
Co-authored-by: ti-srebot <66930949+ti-srebot@users.noreply.github.com>

expression/builtin_control.go

@@ -540,12 +540,10 @@ func (b *builtinIfIntSig) evalInt(row chunk.Row) (ret int64, isNull bool, err er
 	if err != nil {
 		return 0, true, err
 	}
-	arg1, isNull1, err := b.args[1].EvalInt(b.ctx, row)
-	if (!isNull0 && arg0 != 0) || err != nil {
-		return arg1, isNull1, err
+	if !isNull0 && arg0 != 0 {
+		return b.args[1].EvalInt(b.ctx, row)
 	}
-	arg2, isNull2, err := b.args[2].EvalInt(b.ctx, row)
-	return arg2, isNull2, err
+	return b.args[2].EvalInt(b.ctx, row)
 }
 
 type builtinIfRealSig struct {
@@ -563,12 +561,10 @@ func (b *builtinIfRealSig) evalReal(row chunk.Row) (ret float64, isNull bool, er
 	if err != nil {
 		return 0, true, err
 	}
-	arg1, isNull1, err := b.args[1].EvalReal(b.ctx, row)
-	if (!isNull0 && arg0 != 0) || err != nil {
-		return arg1, isNull1, err
+	if !isNull0 && arg0 != 0 {
+		return b.args[1].EvalReal(b.ctx, row)
 	}
-	arg2, isNull2, err := b.args[2].EvalReal(b.ctx, row)
-	return arg2, isNull2, err
+	return b.args[2].EvalReal(b.ctx, row)
 }
 
 type builtinIfDecimalSig struct {
@@ -586,12 +582,10 @@ func (b *builtinIfDecimalSig) evalDecimal(row chunk.Row) (ret *types.MyDecimal,
 	if err != nil {
 		return nil, true, err
 	}
-	arg1, isNull1, err := b.args[1].EvalDecimal(b.ctx, row)
-	if (!isNull0 && arg0 != 0) || err != nil {
-		return arg1, isNull1, err
+	if !isNull0 && arg0 != 0 {
+		return b.args[1].EvalDecimal(b.ctx, row)
 	}
-	arg2, isNull2, err := b.args[2].EvalDecimal(b.ctx, row)
-	return arg2, isNull2, err
+	return b.args[2].EvalDecimal(b.ctx, row)
 }
 
 type builtinIfStringSig struct {
@@ -609,12 +603,10 @@ func (b *builtinIfStringSig) evalString(row chunk.Row) (ret string, isNull bool,
 	if err != nil {
 		return "", true, err
 	}
-	arg1, isNull1, err := b.args[1].EvalString(b.ctx, row)
-	if (!isNull0 && arg0 != 0) || err != nil {
-		return arg1, isNull1, err
+	if !isNull0 && arg0 != 0 {
+		return b.args[1].EvalString(b.ctx, row)
 	}
-	arg2, isNull2, err := b.args[2].EvalString(b.ctx, row)
-	return arg2, isNull2, err
+	return b.args[2].EvalString(b.ctx, row)
 }
 
 type builtinIfTimeSig struct {
@@ -632,12 +624,10 @@ func (b *builtinIfTimeSig) evalTime(row chunk.Row) (ret types.Time, isNull bool,
 	if err != nil {
 		return ret, true, err
 	}
-	arg1, isNull1, err := b.args[1].EvalTime(b.ctx, row)
-	if (!isNull0 && arg0 != 0) || err != nil {
-		return arg1, isNull1, err
+	if !isNull0 && arg0 != 0 {
+		return b.args[1].EvalTime(b.ctx, row)
 	}
-	arg2, isNull2, err := b.args[2].EvalTime(b.ctx, row)
-	return arg2, isNull2, err
+	return b.args[2].EvalTime(b.ctx, row)
 }
 
 type builtinIfDurationSig struct {
@@ -655,12 +645,10 @@ func (b *builtinIfDurationSig) evalDuration(row chunk.Row) (ret types.Duration,
 	if err != nil {
 		return ret, true, err
 	}
-	arg1, isNull1, err := b.args[1].EvalDuration(b.ctx, row)
-	if (!isNull0 && arg0 != 0) || err != nil {
-		return arg1, isNull1, err
+	if !isNull0 && arg0 != 0 {
+		return b.args[1].EvalDuration(b.ctx, row)
 	}
-	arg2, isNull2, err := b.args[2].EvalDuration(b.ctx, row)
-	return arg2, isNull2, err
+	return b.args[2].EvalDuration(b.ctx, row)
 }
 
 type builtinIfJSONSig struct {
@@ -678,21 +666,10 @@ func (b *builtinIfJSONSig) evalJSON(row chunk.Row) (ret json.BinaryJSON, isNull
 	if err != nil {
 		return ret, true, err
 	}
-	arg1, isNull1, err := b.args[1].EvalJSON(b.ctx, row)
-	if err != nil {
-		return ret, true, err
-	}
-	arg2, isNull2, err := b.args[2].EvalJSON(b.ctx, row)
-	if err != nil {
-		return ret, true, err
-	}
-	switch {
-	case isNull0 || arg0 == 0:
-		ret, isNull = arg2, isNull2
-	case arg0 != 0:
-		ret, isNull = arg1, isNull1
+	if !isNull0 && arg0 != 0 {
+		return b.args[1].EvalJSON(b.ctx, row)
 	}
-	return
+	return b.args[2].EvalJSON(b.ctx, row)
 }
 
 type ifNullFunctionClass struct {

expression/constant_fold.go

@@ -56,12 +56,8 @@ func ifFoldHandler(expr *ScalarFunction) (Expression, bool) {
 		}
 		return foldConstant(args[2])
 	}
-	var isDeferred, isDeferredConst bool
-	expr.GetArgs()[1], isDeferred = foldConstant(args[1])
-	isDeferredConst = isDeferredConst || isDeferred
-	expr.GetArgs()[2], isDeferred = foldConstant(args[2])
-	isDeferredConst = isDeferredConst || isDeferred
-	return expr, isDeferredConst
+	// if the condition is not const, which branch is unknown to run, so directly return.
+	return expr, false
 }
 
 func ifNullFoldHandler(expr *ScalarFunction) (Expression, bool) {
@@ -76,18 +72,17 @@ func ifNullFoldHandler(expr *ScalarFunction) (Expression, bool) {
 		}
 		return constArg, isDeferred
 	}
-	var isDeferredConst bool
-	expr.GetArgs()[1], isDeferredConst = foldConstant(args[1])
-	return expr, isDeferredConst
+	// if the condition is not const, which branch is unknown to run, so directly return.
+	return expr, false
 }
 
 func caseWhenHandler(expr *ScalarFunction) (Expression, bool) {
 	args, l := expr.GetArgs(), len(expr.GetArgs())
-	var isDeferred, isDeferredConst, hasNonConstCondition bool
+	var isDeferred, isDeferredConst bool
 	for i := 0; i < l-1; i += 2 {
 		expr.GetArgs()[i], isDeferred = foldConstant(args[i])
 		isDeferredConst = isDeferredConst || isDeferred
-		if _, isConst := expr.GetArgs()[i].(*Constant); isConst && !hasNonConstCondition {
+		if _, isConst := expr.GetArgs()[i].(*Constant); isConst {
 			// If the condition is const and true, and the previous conditions
 			// has no expr, then the folded execution body is returned, otherwise
 			// the arguments of the casewhen are folded and replaced.
@@ -105,20 +100,14 @@ func caseWhenHandler(expr *ScalarFunction) (Expression, bool) {
 				return BuildCastFunction(expr.GetCtx(), foldedExpr, foldedExpr.GetType()), isDeferredConst
 			}
 		} else {
-			hasNonConstCondition = true
+			// for no-const, here should return directly, because the following branches are unknown to be run or not
+			return expr, false
 		}
-		expr.GetArgs()[i+1], isDeferred = foldConstant(args[i+1])
-		isDeferredConst = isDeferredConst || isDeferred
-	}
-
-	if l%2 == 0 {
-		return expr, isDeferredConst
 	}
-
 	// If the number of arguments in casewhen is odd, and the previous conditions
-	// is const and false, then the folded else execution body is returned. otherwise
+	// is false, then the folded else execution body is returned. otherwise
 	// the execution body of the else are folded and replaced.
-	if !hasNonConstCondition {
+	if l%2 == 1 {
 		foldedExpr, isDeferred := foldConstant(args[l-1])
 		isDeferredConst = isDeferredConst || isDeferred
 		if _, isConst := foldedExpr.(*Constant); isConst {
@@ -127,10 +116,6 @@ func caseWhenHandler(expr *ScalarFunction) (Expression, bool) {
 		}
 		return BuildCastFunction(expr.GetCtx(), foldedExpr, foldedExpr.GetType()), isDeferredConst
 	}
-
-	expr.GetArgs()[l-1], isDeferred = foldConstant(args[l-1])
-	isDeferredConst = isDeferredConst || isDeferred
-
 	return expr, isDeferredConst
 }
 

expression/function_traits.go

@@ -56,6 +56,15 @@ var DisableFoldFunctions = map[string]struct{}{
 	ast.Benchmark: {},
 }
 
+// TryFoldFunctions stores functions which try to fold constant in child scope functions if without errors/warnings,
+// otherwise, the child functions do not fold constant.
+// Note: the function itself should fold constant.
+var TryFoldFunctions = map[string]struct{}{
+	ast.If:     {},
+	ast.Ifnull: {},
+	ast.Case:   {},
+}
+
 // IllegalFunctions4GeneratedColumns stores functions that is illegal for generated columns.
 // See https://github.com/mysql/mysql-server/blob/5.7/mysql-test/suite/gcol/inc/gcol_blocked_sql_funcs_main.inc for details
 var IllegalFunctions4GeneratedColumns = map[string]struct{}{

expression/integration_test.go

@@ -2808,6 +2808,24 @@ func (s *testIntegrationSuite2) TestBuiltin(c *C) {
 	tk.MustQuery("select ifnull(b, b/0) from t")
 	tk.MustQuery("show warnings").Check(testkit.Rows())
 
+	tk.MustQuery("select case when 1 then 1 else 1/0 end")
+	tk.MustQuery("show warnings").Check(testkit.Rows())
+	tk.MustQuery(" select if(1,1,1/0)")
+	tk.MustQuery("show warnings").Check(testkit.Rows())
+	tk.MustQuery("select ifnull(1, 1/0)")
+	tk.MustQuery("show warnings").Check(testkit.Rows())
+
+	tk.MustExec("delete from t")
+	tk.MustExec("insert t values ('str2', 0)")
+	tk.MustQuery("select case when b < 1 then 1 else 1/0 end from t")
+	tk.MustQuery("show warnings").Check(testkit.Rows())
+	tk.MustQuery("select case when b < 1 then 1 when 1/0 then b else 1/0 end from t")
+	tk.MustQuery("show warnings").Check(testkit.Rows())
+	tk.MustQuery("select if(b < 1 , 1, 1/0) from t")
+	tk.MustQuery("show warnings").Check(testkit.Rows())
+	tk.MustQuery("select ifnull(b, 1/0) from t")
+	tk.MustQuery("show warnings").Check(testkit.Rows())
+
 	tk.MustQuery("select case 2.0 when 2.0 then 3.0 when 3.0 then 2.0 end").Check(testkit.Rows("3.0"))
 	tk.MustQuery("select case 2.0 when 3.0 then 2.0 when 4.0 then 3.0 else 5.0 end").Check(testkit.Rows("5.0"))
 	tk.MustQuery("select case cast('2011-01-01' as date) when cast('2011-01-01' as date) then cast('2011-02-02' as date) end").Check(testkit.Rows("2011-02-02"))

expression/scalar_function.go

@@ -174,7 +174,9 @@ func typeInferForNull(args []Expression) {
 }
 
 // newFunctionImpl creates a new scalar function or constant.
-func newFunctionImpl(ctx sessionctx.Context, fold bool, funcName string, retType *types.FieldType, args ...Expression) (Expression, error) {
+// fold: 1 means folding constants, while 0 means not,
+// -1 means try to fold constants if without errors/warnings, otherwise not.
+func newFunctionImpl(ctx sessionctx.Context, fold int, funcName string, retType *types.FieldType, args ...Expression) (Expression, error) {
 	if retType == nil {
 		return nil, errors.Errorf("RetType cannot be nil for ScalarFunction.")
 	}
@@ -210,20 +212,36 @@ func newFunctionImpl(ctx sessionctx.Context, fold bool, funcName string, retType
 		RetType:  retType,
 		Function: f,
 	}
-	if fold {
+	if fold == 1 {
 		return FoldConstant(sf), nil
+	} else if fold == -1 {
+		// try to fold constants, and return the original function if errors/warnings occur
+		sc := ctx.GetSessionVars().StmtCtx
+		beforeWarns := sc.WarningCount()
+		newSf := FoldConstant(sf)
+		afterWarns := sc.WarningCount()
+		if afterWarns > beforeWarns {
+			sc.TruncateWarnings(int(beforeWarns))
+			return sf, nil
+		}
+		return newSf, nil
 	}
 	return sf, nil
 }
 
 // NewFunction creates a new scalar function or constant via a constant folding.
 func NewFunction(ctx sessionctx.Context, funcName string, retType *types.FieldType, args ...Expression) (Expression, error) {
-	return newFunctionImpl(ctx, true, funcName, retType, args...)
+	return newFunctionImpl(ctx, 1, funcName, retType, args...)
 }
 
 // NewFunctionBase creates a new scalar function with no constant folding.
 func NewFunctionBase(ctx sessionctx.Context, funcName string, retType *types.FieldType, args ...Expression) (Expression, error) {
-	return newFunctionImpl(ctx, false, funcName, retType, args...)
+	return newFunctionImpl(ctx, 0, funcName, retType, args...)
+}
+
+// NewFunctionTryFold creates a new scalar function with trying constant folding.
+func NewFunctionTryFold(ctx sessionctx.Context, funcName string, retType *types.FieldType, args ...Expression) (Expression, error) {
+	return newFunctionImpl(ctx, -1, funcName, retType, args...)
 }
 
 // NewFunctionInternal is similar to NewFunction, but do not returns error, should only be used internally.

planner/core/expression_rewriter.go

@@ -154,6 +154,7 @@ func (b *PlanBuilder) getExpressionRewriter(ctx context.Context, p LogicalPlan)
 	rewriter.preprocess = nil
 	rewriter.insertPlan = nil
 	rewriter.disableFoldCounter = 0
+	rewriter.tryFoldCounter = 0
 	rewriter.ctxStack = rewriter.ctxStack[:0]
 	rewriter.ctxNameStk = rewriter.ctxNameStk[:0]
 	rewriter.ctx = ctx
@@ -226,6 +227,7 @@ type expressionRewriter struct {
 	// leaving the scope(enable again), the counter will -1.
 	// NOTE: This value can be changed during expression rewritten.
 	disableFoldCounter int
+	tryFoldCounter     int
 }
 
 func (er *expressionRewriter) ctxStackLen() int {
@@ -401,6 +403,16 @@ func (er *expressionRewriter) Enter(inNode ast.Node) (ast.Node, bool) {
 		if _, ok := expression.DisableFoldFunctions[v.FnName.L]; ok {
 			er.disableFoldCounter++
 		}
+		if _, ok := expression.TryFoldFunctions[v.FnName.L]; ok {
+			er.tryFoldCounter++
+		}
+	case *ast.CaseExpr:
+		if _, ok := expression.DisableFoldFunctions["case"]; ok {
+			er.disableFoldCounter++
+		}
+		if _, ok := expression.TryFoldFunctions["case"]; ok {
+			er.tryFoldCounter++
+		}
 	case *ast.SetCollationExpr:
 		// Do nothing
 	default:
@@ -944,6 +956,9 @@ func (er *expressionRewriter) Leave(originInNode ast.Node) (retNode ast.Node, ok
 	case *ast.VariableExpr:
 		er.rewriteVariable(v)
 	case *ast.FuncCallExpr:
+		if _, ok := expression.TryFoldFunctions[v.FnName.L]; ok {
+			er.tryFoldCounter--
+		}
 		er.funcCallToExpression(v)
 		if _, ok := expression.DisableFoldFunctions[v.FnName.L]; ok {
 			er.disableFoldCounter--
@@ -959,7 +974,13 @@ func (er *expressionRewriter) Leave(originInNode ast.Node) (retNode ast.Node, ok
 	case *ast.BetweenExpr:
 		er.betweenToExpression(v)
 	case *ast.CaseExpr:
+		if _, ok := expression.TryFoldFunctions["case"]; ok {
+			er.tryFoldCounter--
+		}
 		er.caseToExpression(v)
+		if _, ok := expression.DisableFoldFunctions["case"]; ok {
+			er.disableFoldCounter--
+		}
 	case *ast.FuncCastExpr:
 		arg := er.ctxStack[len(er.ctxStack)-1]
 		er.err = expression.CheckArgsNotMultiColumnRow(arg)
@@ -1053,6 +1074,9 @@ func (er *expressionRewriter) newFunction(funcName string, retType *types.FieldT
 	if er.disableFoldCounter > 0 {
 		return expression.NewFunctionBase(er.sctx, funcName, retType, args...)
 	}
+	if er.tryFoldCounter > 0 {
+		return expression.NewFunctionTryFold(er.sctx, funcName, retType, args...)
+	}
 	return expression.NewFunction(er.sctx, funcName, retType, args...)
 }