expression: avoid padding 0 when implicitly cast to binary

cmd/explaintest/r/collation_check_use_collation_disabled.result

@@ -128,4 +128,29 @@ select col_25 from tbl_2 where ( tbl_2.col_27 > 'nSWYrpTH' or not( tbl_2.col_27
 col_25
 select col_25 from tbl_2 use index(primary) where ( tbl_2.col_27 > 'nSWYrpTH' or not( tbl_2.col_27 between 'CsWIuxlSjU' and 'SfwoyjUEzgg' ) ) and ( tbl_2.col_23 <= -95);
 col_25
+drop table if exists t1;
+drop table if exists t2;
+create table t1(a char(20));
+create table t2(b binary(20), c binary(20));
+insert into t1 value('-1');
+insert into t2 value(0x2D31, 0x67);
+insert into t2 value(0x2D31, 0x73);
+select a from t1, t2 where t1.a between t2.b and t2.c;
+a
+select a from t1, t2 where cast(t1.a as binary(20)) between t2.b and t2.c;
+a
+-1
+-1
+drop table if exists t1;
+drop table if exists t2;
+create table t1(a char(20)) collate utf8mb4_general_ci;
+create table t2(b binary(20), c char(20)) collate utf8mb4_general_ci;
+insert into t1 values ('a');
+insert into t2 values (0x0, 'A');
+select * from t1, t2 where t1.a between t2.b and t2.c;
+a	b	c
+insert into t1 values ('-1');
+insert into t2 values (0x2d31, '');
+select * from t1, t2 where t1.a in (t2.b, 3);
+a	b	c
 use test

cmd/explaintest/r/collation_check_use_collation_enabled.result

@@ -147,4 +147,29 @@ col_25
 select col_25 from tbl_2 use index(primary) where ( tbl_2.col_27 > 'nSWYrpTH' or not( tbl_2.col_27 between 'CsWIuxlSjU' and 'SfwoyjUEzgg' ) ) and ( tbl_2.col_23 <= -95);
 col_25
 89
+drop table if exists t1;
+drop table if exists t2;
+create table t1(a char(20));
+create table t2(b binary(20), c binary(20));
+insert into t1 value('-1');
+insert into t2 value(0x2D31, 0x67);
+insert into t2 value(0x2D31, 0x73);
+select a from t1, t2 where t1.a between t2.b and t2.c;
+a
+select a from t1, t2 where cast(t1.a as binary(20)) between t2.b and t2.c;
+a
+-1
+-1
+drop table if exists t1;
+drop table if exists t2;
+create table t1(a char(20)) collate utf8mb4_general_ci;
+create table t2(b binary(20), c char(20)) collate utf8mb4_general_ci;
+insert into t1 values ('a');
+insert into t2 values (0x0, 'A');
+select * from t1, t2 where t1.a between t2.b and t2.c;
+a	b	c
+insert into t1 values ('-1');
+insert into t2 values (0x2d31, '');
+select * from t1, t2 where t1.a in (t2.b, 3);
+a	b	c
 use test

cmd/explaintest/t/collation_check_use_collation.test

@@ -86,5 +86,28 @@ insert ignore into tbl_2 values ( 5888267793391993829,5371,94.63,-109,5728076076
 select col_25 from tbl_2 where ( tbl_2.col_27 > 'nSWYrpTH' or not( tbl_2.col_27 between 'CsWIuxlSjU' and 'SfwoyjUEzgg' ) ) and ( tbl_2.col_23 <= -95);
 select col_25 from tbl_2 use index(primary) where ( tbl_2.col_27 > 'nSWYrpTH' or not( tbl_2.col_27 between 'CsWIuxlSjU' and 'SfwoyjUEzgg' ) ) and ( tbl_2.col_23 <= -95);
 
+# check implicit binary collation cast
+drop table if exists t1;
+drop table if exists t2;
+# issue 34823
+create table t1(a char(20));
+create table t2(b binary(20), c binary(20));
+insert into t1 value('-1');
+insert into t2 value(0x2D31, 0x67);
+insert into t2 value(0x2D31, 0x73);
+select a from t1, t2 where t1.a between t2.b and t2.c;
+select a from t1, t2 where cast(t1.a as binary(20)) between t2.b and t2.c;
+# binary collation in single side
+drop table if exists t1;
+drop table if exists t2;
+create table t1(a char(20)) collate utf8mb4_general_ci;
+create table t2(b binary(20), c char(20)) collate utf8mb4_general_ci;
+insert into t1 values ('a');
+insert into t2 values (0x0, 'A');
+select * from t1, t2 where t1.a between t2.b and t2.c;
+insert into t1 values ('-1');
+insert into t2 values (0x2d31, '');
+select * from t1, t2 where t1.a in (t2.b, 3);
+
 # cleanup environment
 use test

expression/builtin_cast.go

@@ -29,6 +29,7 @@ import (
 
 	"github.com/pingcap/errors"
 	"github.com/pingcap/tidb/parser/ast"
+	"github.com/pingcap/tidb/parser/charset"
 	"github.com/pingcap/tidb/parser/model"
 	"github.com/pingcap/tidb/parser/mysql"
 	"github.com/pingcap/tidb/parser/terror"
@@ -1840,6 +1841,15 @@ func BuildCastCollationFunction(ctx sessionctx.Context, expr Expression, ec *Exp
 		} else {
 			return expr
 		}
+	} else if ec.Charset == charset.CharsetBin {
+		// When cast character string to binary string, if we still use fixed length representation,
+		// then 0 padding will be used, which can affect later execution.
+		// e.g. https://github.com/pingcap/tidb/issues/34823.
+		// On the other hand, we can not directly return origin expr back,
+		// since we need binary collation to do string comparison later.
+		// e.g. https://github.com/pingcap/tidb/pull/35053#discussion_r894155052
+		// Here we use VarString type of cast, i.e `cast(a as binary)`, to avoid this problem.
+		tp.SetType(mysql.TypeVarString)
 	}
 	tp.SetCharset(ec.Charset)
 	tp.SetCollate(ec.Collation)

planner/core/expression_rewriter.go

@@ -1557,6 +1557,7 @@ func (er *expressionRewriter) castCollationForIn(colLen int, elemCnt int, stkLen
 		return
 	}
 	for i := stkLen - elemCnt; i < stkLen; i++ {
+		// todo: consider refining the code and reusing expression.BuildCollationFunction here
 		if er.ctxStack[i].GetType().EvalType() == types.ETString {
 			rowFunc, ok := er.ctxStack[i].(*expression.ScalarFunction)
 			if ok && rowFunc.FuncName.String() == ast.RowFunc {
@@ -1573,6 +1574,14 @@ func (er *expressionRewriter) castCollationForIn(colLen int, elemCnt int, stkLen
 				} else {
 					continue
 				}
+			} else if coll.Charset == charset.CharsetBin {
+				// When cast character string to binary string, if we still use fixed length representation,
+				// then 0 padding will be used, which can affect later execution.
+				// e.g. https://github.com/pingcap/tidb/pull/35053#pullrequestreview-1008757770 gives an unexpected case.
+				// On the other hand, we can not directly return origin expr back,
+				// since we need binary collation to do string comparison later.
+				// Here we use VarString type of cast, i.e `cast(a as binary)`, to avoid this problem.
+				tp.SetType(mysql.TypeVarString)
 			}
 			tp.SetCharset(coll.Charset)
 			tp.SetCollate(coll.Collation)