ResolvedCollation¶

Overview¶

ResolvedCollation is a leaf expression that represents a resolved collation name in Spark SQL. It encapsulates a collation identifier that has been resolved during the analysis phase and provides a way to reference specific collation rules for string operations.

Syntax¶

This expression is primarily used internally during query planning and analysis. It's not directly exposed in SQL syntax but represents resolved collation references.

-- Collations are typically specified in column definitions or COLLATE clauses
SELECT col1 COLLATE "UTF8_BINARY" FROM table1

Arguments¶

Argument	Type	Description
collationName	String	The name of the resolved collation (e.g., "UTF8_BINARY")

Return Type¶

Returns a StringType with the collation ID corresponding to the resolved collation name. The collation ID is determined by CollationFactory.collationNameToId(collationName).

Supported Data Types¶

This expression works with string collation names and produces string types with specific collation metadata.

Input: String collation name
Output: StringType with collation metadata

Algorithm¶

The expression evaluation follows these steps:

Stores the resolved collation name as a string parameter
Maps the collation name to a collation ID using CollationFactory
Creates a StringType with the resolved collation ID as metadata
Evaluates to a literal string value containing the collation name
Delegates actual evaluation to a Literal expression for consistency

Partitioning Behavior¶

ResolvedCollation has minimal impact on partitioning behavior:

Does not affect partitioning schemes as it's a leaf expression
Does not require shuffle operations
Preserves existing partitioning since it produces deterministic output

Edge Cases¶

Null handling: The expression is non-nullable (nullable = false)
Invalid collation names: Relies on CollationFactory validation during construction
Code generation: Uses passthrough delegation to Literal expression for consistency
Empty collation names: Behavior depends on CollationFactory implementation
The doGenCode method throws an internal error and should never be called directly

Code Generation¶

Supports Tungsten code generation through delegation. The expression implements genCode() by creating a Literal expression with the collation name and delegating code generation to it. The doGenCode() method is intentionally not implemented and throws an internal error if called directly.

Examples¶

-- ResolvedCollation is used internally when collations are specified
CREATE TABLE example (
  id INT,
  name STRING COLLATE 'UTF8_BINARY'
);

// Internal usage during expression resolution
val resolvedCollation = ResolvedCollation("UTF8_BINARY")
val dataType = resolvedCollation.dataType  // StringType with collation ID
val result = resolvedCollation.eval(InternalRow.empty)  // Evaluates to "UTF8_BINARY"