<a id="ksqldb-reference-data-types"></a>

# Data Types in ksqlDB for Confluent Platform

ksqlDB supports the following built-in data types for declaring
column and expression types.

## Boolean types

| Name      | Description                          | Backing Java type                                                                                        |
|-----------|--------------------------------------|----------------------------------------------------------------------------------------------------------|
| `boolean` | value representing `true` or `false` | [java.lang.Boolean](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Boolean.html) |

## Character types

| Name                | Description                | Backing Java type                                                                                      |
|---------------------|----------------------------|--------------------------------------------------------------------------------------------------------|
| `varchar`, `string` | variable-length string     | [java.lang.String](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/String.html) |
| `bytes`             | variable-length byte array | [byte []](https://docs.oracle.com/javase/8/docs/api/java/lang/Byte.html)                               |

The `varchar` type represents a string in UTF-16 format.

Comparisons between `varchar` instances don’t account for locale.

The `bytes` type represents an array of raw bytes.

## Numeric types

| Name    | Storage size    | Range (min to max value)                 | Notes                           | Backing Java type                                                                                    |
|---------|-----------------|------------------------------------------|---------------------------------|------------------------------------------------------------------------------------------------------|
| int     | 4 bytes         | -2:sup:31 to 2:sup:31-1                  | typical choice for integer      | [Integer](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Integer.html)       |
| bigint  | 8 bytes         | -2:sup:63 to 2:sup:63-1                  | large-range integer             | [Long](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Long.html)             |
| double  | 8 bytes         | 2:sup:-1074† to (2-2:sup:-52)·2:sup:1023 | variable-precision, inexact     | [Double](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Double.html)         |
| decimal | value dependent | n/a                                      | user-specified precision, exact | [BigDecimal](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/math/BigDecimal.html) |

<sub>†</sub> Smallest positive nonzero value

### Integer types

The `int` and `bigint` types store integers, which are numbers
without decimals. Storing values outside of the supported range results
in an error.

If your values are in its range, the `int` type is a good choice,
because its implementation has minimal overhead. If your values may be
of a larger size, use `bigint`.

### Floating-point types

The `double` data type is an inexact, variable-precision numeric type.
The term “inexact” means an approximate value is stored. Storing values
outside of its bounds of capacity will result in an error.

### Valid ranges

Numeric data types have the same valid minimum and maximum values as
their corresponding Java types.

### Arbitrary precision types

The `decimal` type can be used to store fractional numbers with exact
precision. This is useful for modeling money or other values that don’t
tolerate approximate storage representations.

`decimal` types take two parameters: precision and scale. *Precision*
is the maximum total number of decimal digits to be stored, including
values to the left and right of the decimal point. The precision must be
greater than 1. There is no default precision.

*Scale* is the number of decimal digits to the right of the decimal
point. This number must be greater than *0* and less than or equal to
the value for precision.

To declare a column of the `decimal` type, use the syntax:

```sql
DECIMAL(precision, scale)
```

Mathematical operations between `double` and `decimal` cause the
decimal to be converted to a double value automatically. Converting from
the `decimal` data type to any floating point type (`double`) may
cause loss of precision.

- Upcasting an `int` to a `decimal` produces a `decimal` with a
  precision of *10* and a scale of *0*.
- Upcasting a `bigint` to a `decimal` produces a `decimal` with a
  precision of *19* and a scale of *0*.

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## Time types

| Name      | Description                                                         | Backing Java type                                                                                         |
|-----------|---------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------|
| time      | Time of day in millisecond precision                                | [java.sql.Time](https://docs.oracle.com/en/java/javase/11/docs/api/java.sql/java/sql/Time.html)           |
| date      | Calendar date independent of time zone                              | [java.sql.Date](https://docs.oracle.com/en/java/javase/11/docs/api/java.sql/java/sql/Date.html)           |
| timestamp | Point in time in millisecond precision without timezone information | [java.sql.Timestamp](https://docs.oracle.com/en/java/javase/11/docs/api/java.sql/java/sql/Timestamp.html) |

## Compound types

ksqlDB supports the following compound types, which group multiple values
into a single column.

#### NOTE
The `DELIMITED` serialization format doesn’t support compound types.

| Name   | Description                           | Backing Java type                                                                                |
|--------|---------------------------------------|--------------------------------------------------------------------------------------------------|
| array  | Sequence of values of a single type   | [Java native array](https://docs.oracle.com/javase/specs/jls/se11/html/jls-10.html)              |
| map    | A mapping of keys to values           | [java.util.map](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/Map.html) |
| struct | A strongly-typed structured data type | [Struct](/platform/current/connect/javadocs/javadoc/org/apache/kafka/connect/data/Struct.html)   |

### Array

`ARRAY<ElementType>`

ksqlDB supports fields that are arrays of another type. All of the
elements in the array must be of the same type. The element type can be
any valid SQL type.

The elements of an array are one-indexed and can be accessed by using
the `[]` operator passing in the index. For example, `SOME_ARRAY[1]`
retrieves the first element from the array. For more information, see
[Operators](../../developer-guide/ksqldb-reference/operators.md#ksqldb-reference-operators).

You can define arrays within a `CREATE TABLE` or `CREATE STREAM`
statement by using the syntax `ARRAY<ElementType>`. For example,
`ARRAY<INT>` defines an array of integers.

Also, you can output an array from a query by using a SELECT statement.
The following example creates an array from a stream named `s1`.

```sql
SELECT ARRAY[1, 2] FROM s1 EMIT CHANGES;
```

Starting in version 0.7.1, the built-in AS_ARRAY function syntax for
creating arrays doesn’t work. Replace AS_ARRAY with the ARRAY
constructor syntax. For example, replace this legacy query:

```sql
CREATE STREAM OUTPUT AS SELECT cube_explode(as_array(col1, col2)) VAL1, ABS(col3) VAL2 FROM TEST;
```

With this query:

```sql
CREATE STREAM OUTPUT AS SELECT cube_explode(array[col1, col2]) VAL1, ABS(col3) VAL2 FROM TEST;
```

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### Struct

`STRUCT<FieldName FieldType, ...>`

ksqlDB supports fields that are structs. A struct represents strongly
typed structured data. A struct is an ordered collection of named fields
that have a specific type. The field types can be any valid SQL type.

Access the fields of a struct by using the `->` operator. For example,
`SOME_STRUCT->ID` retrieves the value of the struct’s `ID` field;
and `SOME_STRUCT->*` retrieves the values of all fields of
`SOME_STRUCT`. For more information, see
[Operators](../../developer-guide/ksqldb-reference/operators.md#ksqldb-reference-operators).

You can define structs within a `CREATE TABLE` or `CREATE STREAM`
statement by using the syntax `STRUCT<FieldName FieldType, ...>`. For
example, `STRUCT<ID BIGINT, NAME STRING, AGE INT>` defines a struct
with three fields, with the supplied name and type.

Also, you can output a struct from a query by using a SELECT statement.
The following example creates a struct from a stream named `s1`.

```sql
SELECT STRUCT(f1 := v1, f2 := v2) FROM s1 EMIT CHANGES;
```

### Map

`MAP<KeyType, ValueType>`

ksqlDB supports fields that are maps. A map has a key and value type.
All of the keys must be of the same type, and all of the values must
also be of the same type. Currently only `STRING` keys are supported.
The value type can be any valid SQL type.

Access the values of a map by using the `[]` operator and passing in
the key. For example, `SOME_MAP['cost']` retrieves the value for the
entry with key `cost`, or `null` For more information, see
[Operators](../../developer-guide/ksqldb-reference/operators.md#ksqldb-reference-operators).

You can define maps within a `CREATE TABLE` or `CREATE STREAM`
statement by using the syntax `MAP<KeyType, ValueType>`. For example,
`MAP<STRING, INT>` defines a map with string keys and integer values.

Also, you can output a map from a query by using a SELECT statement. The
following example creates a map from a stream named `s1`.

```sql
SELECT MAP(k1:=v1, k2:=v1*2) FROM s1 EMIT CHANGES;
```

## Custom types

ksqlDB supports custom types using the `CREATE TYPE` statements. See
the [CREATE TYPE docs](../../developer-guide/ksqldb-reference/create-type.md#ksqldb-reference-create-type) for more
information.