CAST function in Amazon QLDB

In Amazon QLDB, use the CAST function to evaluate a given expression to a value and convert the value to a specified target data type. If the conversion can't be made, the function returns an error.

Syntax

CAST ( expression AS type )

Arguments

expression

The field name or expression that evaluates to a value that the function converts. Converting null values returns nulls. This parameter can be any of the supported Data types.

type

The name of the target data type for conversion. This parameter can be one of the supported Data types.

Return type

The data type that is specified by the type argument.

Examples

The following examples show the propagation of unknown types (NULL or MISSING).

CAST(null    AS null)    -- null 
CAST(missing AS null)    -- null 
CAST(missing AS missing) -- missing
CAST(null    AS missing) -- missing
CAST(null    AS boolean) -- null (null AS any data type name results in null)
CAST(missing AS boolean) -- missing (missing AS any data type name results in missing)

Any value that is not an unknown type can't be cast to NULL or MISSING.

CAST(true AS null)    -- error 
CAST(true AS missing) -- error
CAST(1    AS null)    -- error
CAST(1    AS missing) -- error

The following examples show casting AS boolean.

CAST(true      AS boolean) -- true no-op
CAST(0         AS boolean) -- false
CAST(1         AS boolean) -- true
CAST(`1e0`     AS boolean) -- true (float)
CAST(`1d0`     AS boolean) -- true (decimal)
CAST('a'       AS boolean) -- false
CAST('true'    AS boolean) -- true (SqlName string 'true')
CAST(`'true'`  AS boolean) -- true (Ion symbol `'true'`)
CAST(`'false'` AS boolean) -- false (Ion symbol `'false'`)

The following examples show casting AS integer.

CAST(true   AS integer) -- 1
CAST(false  AS integer) -- 0
CAST(1      AS integer) -- 1
CAST(`1d0`  AS integer) -- 1
CAST(`1d3`  AS integer) -- 1000
CAST(1.00   AS integer) -- 1
CAST(1.45   AS integer) -- 1
CAST(1.75   AS integer) -- 1
CAST('12'   AS integer) -- 12
CAST('aa'   AS integer) -- error
CAST(`'22'` AS integer) -- 22
CAST(`'x'`  AS integer) -- error

The following examples show casting AS float.

CAST(true   AS float) -- 1e0
CAST(false  AS float) -- 0e0
CAST(1      AS float) -- 1e0
CAST(`1d0`  AS float) -- 1e0
CAST(`1d3`  AS float) -- 1000e0
CAST(1.00   AS float) -- 1e0
CAST('12'   AS float) -- 12e0
CAST('aa'   AS float) -- error
CAST(`'22'` AS float) -- 22e0
CAST(`'x'`  AS float) -- error

The following examples show casting AS decimal.

CAST(true   AS decimal) -- 1.
CAST(false  AS decimal) -- 0.
CAST(1      AS decimal) -- 1.
CAST(`1d0`  AS decimal) -- 1. (REPL printer serialized to 1.)
CAST(`1d3`  AS decimal) -- 1d3
CAST(1.00   AS decimal) -- 1.00
CAST('12'   AS decimal) -- 12.
CAST('aa'   AS decimal) -- error
CAST(`'22'` AS decimal) -- 22.
CAST(`'x'`  AS decimal) -- error

The following examples show casting AS timestamp.

CAST(`2001T`                      AS timestamp) -- 2001T
CAST('2001-01-01T'                AS timestamp) -- 2001-01-01T
CAST(`'2010-01-01T00:00:00.000Z'` AS timestamp) -- 2010-01-01T00:00:00.000Z
CAST(true                         AS timestamp) -- error
CAST(2001                         AS timestamp) -- error

The following examples show casting AS symbol.

CAST(`'xx'`                     AS symbol) -- xx (`'xx'` is an Ion symbol)
CAST('xx'                       AS symbol) -- xx ('xx' is a string)
CAST(42                         AS symbol) -- '42'
CAST(`1e0`                      AS symbol) -- '1.0'
CAST(`1d0`                      AS symbol) -- '1'
CAST(true                       AS symbol) -- 'true'
CAST(false                      AS symbol) -- 'false'
CAST(`2001T`                    AS symbol) -- '2001T'
CAST(`2001-01-01T00:00:00.000Z` AS symbol) -- '2001-01-01T00:00:00.000Z'

The following examples show casting AS string.

CAST(`'xx'`                     AS string) -- "xx" (`'xx'` is an Ion symbol)
CAST('xx'                       AS string) -- "xx" ('xx' is a string)
CAST(42                         AS string) -- "42"
CAST(`1e0`                      AS string) -- "1.0"
CAST(`1d0`                      AS string) -- "1"
CAST(true                       AS string) -- "true"
CAST(false                      AS string) -- "false"
CAST(`2001T`                    AS string) -- "2001T"
CAST(`2001-01-01T00:00:00.000Z` AS string) -- "2001-01-01T00:00:00.000Z"

The following examples show casting AS struct.

CAST(`{ a: 1 }` AS struct) -- {a:1}
CAST(true       AS struct) -- err

The following examples show casting AS list.

CAST(`[1, 2, 3]`        AS list) -- [1,2,3]
CAST(<<'a', { 'b':2 }>> AS list) -- ["a",{'b':2}]
CAST({ 'b':2 }          AS list) -- error

The following examples are runnable statements that include some of the previous examples.

SELECT CAST(true AS integer) FROM << 0 >>            -- 1
SELECT CAST('2001-01-01T' AS timestamp) FROM << 0 >> -- 2001-01-01T
SELECT CAST('xx' AS symbol) FROM << 0 >>             -- xx
SELECT CAST(42 AS string) FROM << 0 >>               -- "42"

Related functions

• TO_STRING

• TO_TIMESTAMP