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Snowflake: Improve translation of FROM clauses #442

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Jun 7, 2024
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Snowflake: Improve translation of FROM clauses #442

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2 changes: 1 addition & 1 deletion core/src/main/antlr4/com/databricks/labs/remorph/parsers/snowflake/SnowflakeParser.g4
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Original file line number Diff line number Diff line change
Expand Up @@ -4036,7 +4036,7 @@ from_clause
;

table_sources
: table_source (COLON table_source)*
: table_source (COMMA table_source)*
;

table_source
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15 changes: 15 additions & 0 deletions ...c/main/scala/com/databricks/labs/remorph/parsers/snowflake/SnowflakeRelationBuilder.scala
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Expand Up @@ -72,6 +72,17 @@ class SnowflakeRelationBuilder extends SnowflakeParserBaseVisitor[ir.Relation] w
buildHaving(ctx.having_clause(), buildGroupBy(ctx.group_by_clause(), buildWhere(ctx.where_clause(), from)))))
}

override def visitFrom_clause(ctx: From_clauseContext): ir.Relation = {
val tableSources = ctx.table_sources().table_source().asScala.map(_.accept(this))
// The tableSources seq cannot be empty (as empty FROM clauses are not allowed
tableSources match {
case Seq(tableSource) => tableSource
case sources =>
sources.reduce(
ir.Join(_, _, None, ir.InnerJoin, Seq(), ir.JoinDataType(is_left_struct = false, is_right_struct = false)))
}
}

private def buildFilter[A](ctx: A, conditionRule: A => ParserRuleContext, input: ir.Relation): ir.Relation =
Option(ctx).fold(input) { c =>
ir.Filter(input, conditionRule(c).accept(new SnowflakeExpressionBuilder(new SnowflakeFunctionBuilder)))
Expand Down Expand Up @@ -123,6 +134,10 @@ class SnowflakeRelationBuilder extends SnowflakeParserBaseVisitor[ir.Relation] w
ctx.values_table().values_table_body().accept(this)
}

override def visitObjRefSubquery(ctx: ObjRefSubqueryContext): ir.Relation = {
val subquery = ctx.subquery().accept(this)
Option(ctx.as_alias()).map(a => ir.SubqueryAlias(subquery, a.alias().getText, "")).getOrElse(subquery)
}
override def visitValues_table_body(ctx: Values_table_bodyContext): ir.Relation = {
val expressionBuilder = new SnowflakeExpressionBuilder(new SnowflakeFunctionBuilder)
val expressions =
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14 changes: 14 additions & 0 deletions ...st/scala/com/databricks/labs/remorph/parsers/snowflake/SnowflakeRelationBuilderSpec.scala
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Expand Up @@ -19,6 +19,20 @@ class SnowflakeRelationBuilderSpec extends AnyWordSpec with SnowflakeParserTestC

"translate FROM clauses" in {
example("FROM some_table", _.from_clause(), namedTable("some_table"))
example(
"FROM t1, t2, t3",
_.from_clause(),
Join(
Join(namedTable("t1"), namedTable("t2"), None, InnerJoin, Seq(), JoinDataType(false, false)),
namedTable("t3"),
None,
InnerJoin,
Seq(),
JoinDataType(false, false)))
example(
"FROM (SELECT * FROM t1) t2",
_.from_clause(),
SubqueryAlias(Project(namedTable("t1"), Seq(Star(None))), "t2", ""))
}

"translate WHERE clauses" in {
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