Describe show commands

[YANG-DB]

Description

Support PPL Describe command

Issues Resolved

#527

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[LantaoJin]

change to describe flint_ppl_test

[LantaoJin]

And here:

            return context.with(
                new DescribeTableCommand(
                    new TableIdentifier(node.getTableQualifiedName().toString()),
                    scala.collection.immutable.Map$.MODULE$.<String, String>empty(),
                    false,
                    DescribeRelation$.MODULE$.getOutputAttrs()));

[YANG-DB]

@LantaoJin thanks!!

[LantaoJin]

@YANG-DB to make this IT test successful.
The expectedPlan should change as following either.

      val expectedPlan: LogicalPlan =
        DescribeTableCommand(
          TableIdentifier("flint_ppl_test"),
          Map.empty[String, String],
          isExtended = false,
          output = DescribeRelation.getOutputAttrs)

[LantaoJin]

Oh, we miss testing the table_identifier with quoted.

Seq("flint_ppl_test", "`flint_ppl_test`").foreach { table =>
  val frame = sql(s"""
     describe $table

[YANG-DB]

yes probably need to add some more fail based use cases...

[LantaoJin]

I checked the spark sql reference. The DESCRIBE command syntax is DESCRIBE [ database_name. ] table_name.
So to support database prefix, here need additional modification:

            TableIdentifier identifier;
            if (node.getTableQualifiedName().getParts().size() == 1) {
                identifier = new TableIdentifier(node.getTableQualifiedName().getParts().get(0));
            } else if (node.getTableQualifiedName().getParts().size() == 2) {
                identifier = new TableIdentifier(
                    node.getTableQualifiedName().getParts().get(1),
                    Option$.MODULE$.apply(node.getTableQualifiedName().getParts().get(0)));
            } else {
                throw new IllegalArgumentException("Invalid table name: " + node.getTableQualifiedName()
                    + " Syntax: [ database_name. ] table_name");
            }
            return context.with(
                new DescribeTableCommand(
                    identifier,
                    scala.collection.immutable.Map$.MODULE$.<String, String>empty(),
                    false,
                    DescribeRelation$.MODULE$.getOutputAttrs()));

[LantaoJin]

Then we can test on Seq("flint_ppl_test", "`flint_ppl_test`", "default.flint_ppl_test", "`default`.`flint_ppl_test`")

[YANG-DB]

@LantaoJin thanks again