DateFromUnixDate¶

Overview¶

The DateFromUnixDate expression converts a Unix date integer (days since epoch) to a SQL DATE value. It takes an integer representing the number of days since January 1, 1970 (Unix epoch) and returns the corresponding date.

Syntax¶

date_from_unix_date(unix_date)

Arguments¶

Argument	Type	Description
unix_date	INTEGER	Number of days since Unix epoch (1970-01-01)

Return Type¶

DATE - Returns a date value representing the calculated date.

Supported Data Types¶

Input: IntegerType only
The expression uses implicit casting to convert compatible numeric types to integers

Algorithm¶

Takes the input integer value representing days since Unix epoch
Performs null-safety check on the input value
Returns the integer value directly as the internal representation (Spark internally stores dates as days since epoch)
No actual date conversion computation is needed since Spark's internal date representation matches the input format
Code generation creates optimized bytecode that simply passes through the input value

Partitioning Behavior¶

Preserves partitioning as this is a deterministic unary transformation
Does not require shuffle operations
Can be pushed down to individual partitions independently

Edge Cases¶

Null handling: Returns null for null input values (nullIntolerant = true means null inputs produce null outputs)
Integer overflow: Subject to standard integer overflow limitations of the input type
Negative values: Accepts negative integers representing dates before Unix epoch
Out of range dates: May produce invalid dates for extremely large positive or negative integers

Code Generation¶

This expression supports full code generation (Tungsten). The doGenCode method uses defineCodeGen with a simple pass-through function, generating optimized bytecode that directly copies the input value without interpretation overhead.

Examples¶

-- Convert Unix date to actual date
SELECT date_from_unix_date(1);
-- Result: 1970-01-02

-- Convert multiple Unix dates
SELECT date_from_unix_date(0), date_from_unix_date(365), date_from_unix_date(-1);  
-- Result: 1970-01-01, 1971-01-01, 1969-12-31

-- Handle null input
SELECT date_from_unix_date(NULL);
-- Result: NULL

// DataFrame API usage
import org.apache.spark.sql.functions.expr

df.select(expr("date_from_unix_date(unix_day_column)"))

// Using with literal values
df.select(expr("date_from_unix_date(1)").as("epoch_plus_one"))