Impala type conversion functions

Function reference:

Impala supports the following type conversion functions:

• CAST
• TYPEOF

CAST(expression AS type)

Purpose: Returns expression converted to the type data type.

If the expression value is of a type that cannot be converted to the target type:

• Of DECIMAL, DATE, and BOOLEAN, the function returns an error.
• Of all other types, the function returns NULL.

Usage notes:

Use CAST when passing a column value or literal to a function that expects a parameter with a different type. Frequently used in SQL operations such as CREATE TABLE AS SELECT and INSERT ... VALUES to ensure that values from various sources are of the appropriate type for the destination columns.

Where practical, do a one-time CAST() operation during the ingestion process to make each column into the appropriate type, rather than using many CAST() operations in each query; doing type conversions for each row during each query can be expensive for tables with millions or billions of rows.

The way this function deals with time zones when converting to or from TIMESTAMP values is affected by the ‑‑use_local_tz_for_unix_timestamp_conversions startup flag for the impalad daemon. See TIMESTAMP data type for details about how Impala handles time zone considerations for the TIMESTAMP data type.

CAST(expression AS type FORMAT pattern)

Purpose: Returns expression converted to the type data type based on the pattern format string. This signature of CAST() with the FORMAT clause is supported only for casts between STRING / CHAR / VARCHAR types and TIMESTAMP / DATE types.

The following rules apply to pattern. Any exceptions to these rules are noted in the Details column of the table below.

• pattern is a case-insensitive STRING.
• If pattern is NULL, an empty string, or a number, an error returns.
• A fewer digits in expression than specified in the pattern is accepted if a separator is correctly specified in the pattern. For example, CAST('5-01-2017' AS DATE FORMAT 'MM-dd-yyyy') returns DATE'2017-05-01'.
• If fewer number of digits are in expression than specified in the pattern, the current date is used to complete the year pattern. For example, CAST('19/05' AS DATE FORMAT 'YYYY/MM') will return DATE'2019-05-01' when executed on August 8, 2019.

The following format patterns are supported in the FORMAT clause.

Pattern	Description	Details
YYYY	4-digit year.
YYY	Last 3 digits of a year.
YY	Last 2 digits of a year.
Y	Last digit of a year
RRRR	4-digit round year	If 1, 3 or 4-digit year values are provided in expression, treated as YYYY. If 2-digit years are provided in expression, treated as RR. For datetime to string conversions, treated as YYYY. If YYYY, YYY, YY, Y, or RR is given in the same pattern for a string to datetime conversion, an error returns.
RR	2-digit round year.	For datetime to string conversion, same as YY. For string to datetime conversions, the first 2 digits of the year in the return value depends on the specified two-digit year and the last two digits of the current year as follows: If the specified 2-digit year is 00 to 49: If the last 2 digits of the current year are 00 to 49, the returned year has the same first 2 digits as the current year. If the last 2 digits of the current year are 50 to 99, the first 2 digits of the returned year are 1 greater than the first 2 digits of the current year. If the specified 2-digit year is 50 to 99: If the last 2 digits of the current year are 00 to 49, the first 2 digits of the returned year are 1 less than the first 2 digits of the current year. If the last 2 digits of the current year are 50 to 99, the returned year has the same first 2 digits as the current year. If YYYY, YYY, YY, Y, or RR is given in the same pattern for a string to datetime conversion, an error returns. If 1-digit year values are provided in expression, it is treated as YYYY.
MM	Month	In datetime to string conversions, 1-digit month is prefixed with a zero.
DD	Day of month (1-31)	In datetime to string conversions, one digit day is prefixed with a zero.
DDD	Day of year (1-366)	In string to datetime conversions, providing MM and DD along with DDD results an error, e.g. YYYY-MM-DDD.
HH HH12	Hour of day (1-12)	In datetime to string conversions, 1-digit hours are prefixed with a zero. If provided hour in expression is not between 1 and 12, returns an error. If no AM/PM is provided in expression, the default is AM.
HH24	Hour of day (0-23)	In string to datetime conversions, if HH12, AM, PM are given in the same pattern, an error returns.
MI	Minute of hour (0-59)	In datetime to string conversions, 1-digit minutes are prefixed with a zero.
SS	Second of minute (0-59)	In datetime to string conversions, 1-digit seconds are prefixed with a zero.
SSSSS	Second of Day (0-86399)	In string to timestamp conversions, if SS, HH, HH12, HH24, MI, AM/PM are given in the same pattern, an error returns.
FF FF1, ..., FF9	Fractional second	A number, 1 to 9, can be used to indicate the number of digits. FF specifies a 9 digits fractional second.
AM PM A.M. P.M.	Meridiem indicator	For datetime to string conversions, AM and PM are treated as synonyms. For example, casting '2019-01-01 11:00 am' to TIMESTAMP with the 'YYYY-MM-DD HH12:MI PM' pattern returns 01-JAN-19 11.00.00.000000 AM. For string to datetime conversion, HH24 in the same pattern returns an error.
TZH	Timezone offset hour	An optional sign, + or -, and 2 digits for the value of signed numbers are allowed for the source expression, e.g. “+10”, “-05”, "04".
TZM	Timezone offset minute	Unsigned numbers are allowed for the source expression.
- . / , ' ; : <space>	Separator	For string to datetime conversions, any separator character in the pattern string would match any separator character in the input expression. For example, CAST(“20191010” AS DATE FORMAT “YYYY-MM-DD”) returns an error, but CAST("2019-.;10 10" AS DATE FORMAT "YYYY-MM-DD") succeeds.
T	Separates the date from the time.	This pattern is used for accepting ISO 8601 datetime formats. Example: YYYY-MM-DDTHH24:MI:SS.FF9Z
Z	Indicates the zero hour offset from UTC.	This pattern is used for accepting ISO 8601 datetime formats.

Examples:

Input	Output
CAST("02-11-2014" AS DATE FORMAT 'dd-mm-yyyy')	2014-11-02
CAST("365 2014" AS DATE FORMAT 'DDD-YYYY')	2014-12-31
CAST("5-01-26" AS DATE FORMAT 'YY-MM-DD')	Executed at 2019-01-01 11:11:11: 2015-01-26
CAST('2018-11-10T15:11:04Z' AS TIMESTAMP FORMAT 'YYYY-MM-DDTHH24:MI:SSZ')	2018-11-10 15:11:04
CAST("95-01-28" AS DATE FORMAT 'YYY-MM-DD')	Executed at 2019-01-01 11:11:11: 2095-01-28
CAST("49-01-15" AS DATE FORMAT 'RR-MM-DD')	Round year when last 2 digits of current year is greater than 49. Executed at 2099-01-01 11:11:11: 2149-01-15
CAST('2019.10.10 13:30:40.123456 +01:30' AS TIMESTAMP FORMAT 'YYYY-MM-DD HH24:MI:SS.FF9 TZH:TZM')	2019-10-10 13:30:40.123456000

TYPEOF(expression)

Purpose: Returns the name of the data type corresponding to expression. For types with extra attributes, such as length for CHAR and VARCHAR, or precision and scale for DECIMAL, includes the full specification of the type.

Return type: STRING

Usage notes: Typically used in interactive exploration of a schema, or in application code that programmatically generates schema definitions such as CREATE TABLE statements, for example, to get the type of an expression such as col1 / col2 or CONCAT(col1, col2, col3). This function is especially useful for arithmetic expressions involving DECIMAL types because the precision and scale of the result is can be different than that of the operands.

Examples:

TYPEOF(2) returns TINYINT.

TYPEOF(NOW()) returns TIMESTAMP.