# NULL functions¶

## IsNull¶

The IsNull function tests if the value of an expression is NULL and if so, returns -1 (True), otherwise 0 (False).

`IsNull( expr )`

Tip

A string with length zero is not considered as a NULL and will cause IsNull to return False.

In this example, an inline table with four rows is loaded, where the first three lines contain either nothing, - or 'NULL' in the Value column. We convert these values to true NULL value representations with the middle preceding LOAD using the Null function.

The first preceding LOAD adds a field checking if the value is NULL,using the IsNull function.

```NullsDetectedAndConverted:
If(IsNull(ValueNullConv), 'T', 'F') as IsItNull;

If(len(trim(Value))= 0 or Value='NULL' or Value='-', Null(), Value ) as ValueNullConv;

[ID, Value
0,
1,NULL
2,-
3,Value];
```

This is the resulting table. In the ValueNullConv column, the NULL values are represented by -.

ID Value ValueNullConv IsItNull
0 - T
1 NULL - T
2 - - T
3 Value Value F

## NULL¶

The Null function returns a NULL value.

`Null( )`

In this example, an inline table with four rows is loaded, where the first three lines contain either nothing, - or 'NULL' in the Value column. We want to convert these values to true NULL value representations.

The middle preceding LOAD performs the conversion using the Null function.

The first preceding LOAD adds a field checking if the value is NULL, just for illustration purposes in this example.

```NullsDetectedAndConverted:
If(IsNull(ValueNullConv), 'T', 'F') as IsItNull;

LOAD *, If(len(trim(Value))= 0 or Value='NULL' or Value='-', Null(), Value ) as ValueNullConv;

[ID, Value
0,
1,NULL
2,-
3,Value];
```

This is the resulting table. In the ValueNullConv column, the NULL values are represented by -.

ID Value ValueNullConv IsItNull
0 - T
1 NULL - T
2 - - T
3 Value Value F