SQL 92 Case Expression Support

[codesplode]

Description

Adds common support for the SQL 92 case expression. Expressions of both common formats are supported.

Supported SQL

CASE With Primary Operand / Condition

SQL:

CASE (yesOrNo)
WHEN ('yes') THEN 1
ELSE 0
END

CASE Without Primary Operand / Condition

CASE
WHEN (yesOrNo = 'yes') THEN 1
WHEN (yesOrNo = 'no') THEN 0
ELSE -1
END

Kotlin Example

Taken from unit tests.

/*
 * Note the use of the word "Clause" to avoid reserved words.
 */
select(
	case<String>(literal(5)) {
		whenClause(literal(6)).thenClause(literal("false"))
		whenClause(literal(5)).thenClause(literal("true"))
		whenClause(literal(4)).thenClause(literal("false"))
		elseClause(literal("false"))
	}
)

Testing

A basic test case was added for this functionality, but could be improved to include more varying conditions, though this may not be necessary because it is ultimately using Expression<*>s for most functionality related to the conditions and values.

Edited to include a kotlin example from unit tests