fixup

expression/builtin_compare.go

@@ -1556,6 +1556,43 @@ func RefineComparedConstant(ctx sessionctx.Context, targetFieldType types.FieldT
 	return con, false
 }
 
+// Since the argument refining of cmp functions can bring some risks to the plan-cache, the optimizer
+// needs to decide to whether to skip the refining or skip plan-cache for safety.
+// For example, `unsigned_int_col > ?(-1)` can be refined to `True`, but the validation of this result
+// can be broken if the parameter changes to 1 after.
+func allowCmpArgsRefining4PlanCache(ctx sessionctx.Context, args []Expression) (allowRefining bool) {
+	if !MaybeOverOptimized4PlanCache(ctx, args) {
+		return true // plan-cache disabled or no parameter in these args
+	}
+
+	// For these 2 cases below, we skip the refining:
+	// 1. year-expr <cmp> const
+	// 2. int-expr <cmp> string/float/double/decimal-const
+	for conIdx := 0; conIdx < 2; conIdx++ {
+		if _, isCon := args[conIdx].(*Constant); !isCon {
+			continue // not a constant
+		}
+
+		// case 1: year-expr <cmp> const
+		// refine `year < 12` to `year < 2012` to guarantee the correctness.
+		// see https://github.com/pingcap/tidb/issues/41626 for more details.
+		exprType := args[1-conIdx].GetType()
+		if exprType.GetType() == mysql.TypeYear {
+			ctx.GetSessionVars().StmtCtx.SkipPlanCache = true
+			return true
+		}
+
+		conType := args[conIdx].GetType().EvalType()
+		if exprType.EvalType() == types.ETInt &&
+			(conType == types.ETString || conType == types.ETReal || conType == types.ETDecimal) {
+			ctx.GetSessionVars().StmtCtx.SkipPlanCache = true
+			return true
+		}
+	}
+
+	return false
+}
+
 // refineArgs will rewrite the arguments if the compare expression is `int column <cmp> non-int constant` or
 // `non-int constant <cmp> int column`. E.g., `a < 1.1` will be rewritten to `a < 2`. It also handles comparing year type
 // with int constant if the int constant falls into a sensible year representation.
@@ -1565,25 +1602,17 @@ func (c *compareFunctionClass) refineArgs(ctx sessionctx.Context, args []Express
 	arg0Type, arg1Type := args[0].GetType(), args[1].GetType()
 	arg0IsInt := arg0Type.EvalType() == types.ETInt
 	arg1IsInt := arg1Type.EvalType() == types.ETInt
-	arg0IsString := arg0Type.EvalType() == types.ETString
-	arg1IsString := arg1Type.EvalType() == types.ETString
 	arg0, arg0IsCon := args[0].(*Constant)
 	arg1, arg1IsCon := args[1].(*Constant)
 	isExceptional, finalArg0, finalArg1 := false, args[0], args[1]
 	isPositiveInfinite, isNegativeInfinite := false, false
-	if MaybeOverOptimized4PlanCache(ctx, args) {
-		// To keep the result be compatible with MySQL, refine `int non-constant <cmp> str constant`
-		// here and skip this refine operation in all other cases for safety.
-		if (arg0IsInt && !arg0IsCon && arg1IsString && arg1IsCon) || (arg1IsInt && !arg1IsCon && arg0IsString && arg0IsCon) {
-			ctx.GetSessionVars().StmtCtx.SkipPlanCache = true
-			RemoveMutableConst(ctx, args)
-		} else {
-			return args
-		}
-	} else if ctx.GetSessionVars().StmtCtx.SkipPlanCache {
-		// We should remove the mutable constant for correctness, because its value may be changed.
-		RemoveMutableConst(ctx, args)
+
+	if !allowCmpArgsRefining4PlanCache(ctx, args) {
+		return args
 	}
+	// We should remove the mutable constant for correctness, because its value may be changed.
+	RemoveMutableConst(ctx, args)
+
 	// int non-constant [cmp] non-int constant
 	if arg0IsInt && !arg0IsCon && !arg1IsInt && arg1IsCon {
 		arg1, isExceptional = RefineComparedConstant(ctx, *arg0Type, arg1, c.op)