# Considerations for data types
<a name="data-types-considerations"></a>

## Size limits
<a name="data-types-considerations-size"></a>

For data types that do not specify a size limit, keep in mind that there is a practical limit of 32MB for all of the data in a single row. For more information, see [Row or column size limitation](other-notable-limitations.md#sql-limitations-rowsize) in [Considerations and limitations for SQL queries in Amazon Athena](other-notable-limitations.md).

## CHAR and VARCHAR
<a name="data-types-considerations-char"></a>

A `CHAR(n)` value always has a count of `n` characters. For example, if you cast 'abc' to `CHAR(7)`, 4 trailing spaces are added. 

Comparisons of `CHAR` values include leading and trailing spaces. 

If a length is specified for `CHAR` or `VARCHAR`, strings are truncated at the specified length when read. If the underlying data string is longer, the underlying data string remains unchanged.

To escape a single quote in a `CHAR` or `VARCHAR`, use an additional single quote.

To cast a non-string data type to a string in a DML query, cast to the `VARCHAR` data type.

To use the `substr` function to return a substring of specified length from a `CHAR` data type, you must first cast the `CHAR` value as a `VARCHAR`. In the following example, `col1` uses the `CHAR` data type.

```
substr(CAST(col1 AS VARCHAR), 1, 4)
```

## DECIMAL
<a name="data-types-considerations-decimal"></a>

To specify decimal values as literals in `SELECT` queries, such as when selecting rows with a specific decimal value, you can specify the `DECIMAL` type and list the decimal value as a literal in single quotes in your query, as in the following examples.

```
SELECT * FROM my_table
WHERE decimal_value = DECIMAL '0.12'
```

```
SELECT DECIMAL '44.6' + DECIMAL '77.2'
```