# [Known Issues] NULLIF report  unsupported type null .md

## Key Words

TiKV, nullif, Unsupported type: Null

## Description

When try to use "select xx from table where nullif(xx)", it will return errors like "Unsupported type: Null"

## Root Cause

`NULL` is not a supported type of the tikv coprocessor, please refer to [https://github.com/tikv/tikv/pull/9632](https://github.com/tikv/tikv/pull/9632)

## Diagnostic Steps

```sql
mysql> create table t12(id char(10));
Query OK, 0 rows affected (0.08 sec)

mysql> insert t12 value(null);
Query OK, 1 row affected (0.02 sec)

mysql> select * from t12 where nullif(t12.id, '');
ERROR 1105 (HY000): other error: [components/tidb_query/src/batch/runner.rs:83]: BatchSelectionExecutor: Evaluate error: [components/tidb_query/src/rpn_expr/types/expr_builder.rs:26]: Unsupported type: Null

mysql> select count(null) from t12;
ERROR 1105 (HY000): other error: [components/tidb_query/src/batch/runner.rs:83]: BatchSelectionExecutor: Evaluate error: [components/tidb_query/src/rpn_expr/types/expr_builder.rs:26]: Unsupported type: Null
```

> **注意**
>  
> the column type should be char or varchar.** 

## Resolution

Upgrade to v5.0.

## Workaround

Add the if function to the pushdown_blacklist, but it may cause impact to the performance.

```sql
mysql> insert mysql.expr_pushdown_blacklist values ('if', 'tikv', '');
mysql> admin reload expr_pushdown_blacklist; 
```

## Affected Version

< 5.0