feat: EXPOSED-334 Support MERGE statement

[obabichevjb]

No description provided.

[bog-walk]

Very happy with the state of the source API.
Left some general comments, but mostly about testing.

[bog-walk]

What's the reason for testing with an IdTable like this and not just a regular Table with a primary key?

[obabichevjb]

It was on purpose, I wanted to have table without id auto generation, to put the values I want and check that they are presented after merge (to test that ON condition is generated correctly)

[e5l]

It looks like MergeBaseStatement.WhenBranchData is not readable as a standalone. It should always be used together and meaningful when reading.

What do you think about MergeStatement.WithWhen or just MergeStatement.When?

@bog-walk, what do you think?

[obabichevjb]

It's quite often referenced as clause in the documentations. So another options might be Clause or WhenClause

[bog-walk]

@e5l @obabichevjb MergeStatement.When and MergeStatement.WhenClause to me seem the most descriptive and to the point when used alone.
If we also want to keep it inline with the MergeWhenAction enum passed to it, for example, then simply MergeStatement.When would work well.

[obabichevjb]

Updated MR, removed any usages of the term "branch" and replaced it with the term "clause".

After 2 iterations I come up with the variant of usage only term "clause(s)" instead of "when"/"whenClauses". It may look more descriptive and simpler in the context of merge command, because there is only one term. With that variant interface of FunctionProvider.merge() looks like:

open fun merge(
    dest: Table,
    source: Table,
    transaction: Transaction,
    clauses: List<MergeStatement.Clause>,
    on: Op<Boolean>?
)

And the Clause data class:

data class Clause(
  val action: ClauseAction,
  val arguments: List<Pair<Column<*>, Any?>>,
  val and: Op<Boolean>?,
  /** ... */
  val deleteWhere: Op<Boolean>? = null
)

enum class ClauseAction {
  INSERT, UPDATE, DELETE
}

Minor but also action parameter of Clause class moved to the first position, as it defines the meaning of the following arguments.

What do you think about such a variant?

One commit before there is an option with MergeStatement.When data class, but I found out that it looks quite weird for the list parameters to call them whens or whenClauses