planner: refine collation handling for between (#30793)

expression/builtin_cast.go

@@ -1826,6 +1826,17 @@ func BuildCastFunction4Union(ctx sessionctx.Context, expr Expression, tp *types.
 	return BuildCastFunction(ctx, expr, tp)
 }
 
+// BuildCastCollationFunction builds a ScalarFunction which casts the collation.
+func BuildCastCollationFunction(ctx sessionctx.Context, expr Expression, ec *ExprCollation) Expression {
+	if expr.GetType().Collate == ec.Collation {
+		return expr
+	}
+	tp := expr.GetType().Clone()
+	tp.Charset, tp.Collate = ec.Charset, ec.Collation
+	newExpr := BuildCastFunction(ctx, expr, tp)
+	return newExpr
+}
+
 // BuildCastFunction builds a CAST ScalarFunction from the Expression.
 func BuildCastFunction(ctx sessionctx.Context, expr Expression, tp *types.FieldType) (res Expression) {
 	expr = TryPushCastIntoControlFunctionForHybridType(ctx, expr, tp)

planner/core/expression_rewriter.go

@@ -1686,19 +1686,19 @@ func (er *expressionRewriter) betweenToExpression(v *ast.BetweenExpr) {
 		return
 	}
 
+	expr = expression.BuildCastCollationFunction(er.sctx, expr, coll)
+	lexp = expression.BuildCastCollationFunction(er.sctx, lexp, coll)
+	rexp = expression.BuildCastCollationFunction(er.sctx, rexp, coll)
+
 	var l, r expression.Expression
-	l, er.err = expression.NewFunctionBase(er.sctx, ast.GE, &v.Type, expr, lexp)
+	l, er.err = expression.NewFunction(er.sctx, ast.GE, &v.Type, expr, lexp)
 	if er.err != nil {
 		return
 	}
-	r, er.err = expression.NewFunctionBase(er.sctx, ast.LE, &v.Type, expr, rexp)
+	r, er.err = expression.NewFunction(er.sctx, ast.LE, &v.Type, expr, rexp)
 	if er.err != nil {
 		return
 	}
-	l.SetCharsetAndCollation(coll.Charset, coll.Collation)
-	r.SetCharsetAndCollation(coll.Charset, coll.Collation)
-	l = expression.FoldConstant(l)
-	r = expression.FoldConstant(r)
 	function, err := er.newFunction(ast.LogicAnd, &v.Type, l, r)
 	if err != nil {
 		er.err = err