Function getNullableJoinSources

packages/db/src/query/optimizer.ts:329–349

* Returns the set of source aliases that are on the nullable side of outer joins. * * For a LEFT join the joined (right) side is nullable. * For a RIGHT join the main (left/from) side is nullable. * For a FULL join both sides are nullable. * * WHERE clauses that reference only a nullable sourc

(query: QueryIR)

 * incorrectly survive residual filtering.
 */
function getNullableJoinSources(query: QueryIR): Set<string> {
  const nullable = new Set<string>()
  if (query.join) {
    const leftAliases = new Set(
      getFromSources(query.from).map((source) => source.alias),
    )
    for (const join of query.join) {
      const joinedAlias = join.from.alias
      if (join.type === `left` || join.type === `full`) {
        nullable.add(joinedAlias)
      }
      if (join.type === `right` || join.type === `full`) {
        for (const leftAlias of leftAliases) {
          nullable.add(leftAlias)
        }
      }
      leftAliases.add(joinedAlias)
    }
  }
  return nullable
}

/**
 * Applies recursive predicate pushdown optimization.