DESCRIBE should accept optional TABLE keyword

[fupelaqu]

Description

The SQL parser requires DESC TABLE <name> or DESCRIBE TABLE <name> with the TABLE keyword mandatory. However, tools like Apache Superset send DESC <name> without the TABLE keyword, which is the standard MySQL/PostgreSQL syntax.

Similarly, DESC <view_name> should work for materialized views when no qualifier is provided.

Example

-- Currently accepted
DESC TABLE ecommerce
DESCRIBE TABLE ecommerce

-- Should also be accepted (TABLE keyword optional)
DESC ecommerce
DESCRIBE ecommerce

Expected Behaviour

The TABLE keyword should be optional in DESCRIBE/DESC statements. When omitted, the parser should default to describing a table (or resolve to a materialized view if no table matches).

Impact

• Superset compatibility: Superset sends DESC <name> via SQL Lab, which fails with a parse error
• User convenience: DESC ecommerce is the most natural syntax
• MySQL/PostgreSQL parity: both accept DESC <name> without qualifier

Implementation Notes

Parser change

In Parser.scala, make TABLE optional in describeTable:

def describeTable: PackratParser[DescribeTable] =
  (("DESCRIBE" | "DESC") ~ opt("TABLE")) ~ ident ^^ { case _ ~ table =>
    DescribeTable(table)
  }

Grammar ordering (critical)

In dqlStatement, the describe parsers must be reordered so that more specific forms are tried before the now-generic describeTable:

describeMaterializedView |  // DESC MATERIALIZED VIEW x — most specific
describePipeline |          // DESC PIPELINE x
describeTable |             // DESC [TABLE] x — least specific (fallback)

Without this reordering, DESC PIPELINE foo would be incorrectly captured by describeTable (treating PIPELINE as a table name).

Current order in dqlStatement

describeTable |           // line 910
...
describePipeline |        // line 914
...
describeMaterializedView  // line 919

Required order

describeMaterializedView |
describePipeline |
describeTable |

Files to modify

File	Change
sql/.../parser/Parser.scala	Make TABLE optional in describeTable, reorder describe parsers in dqlStatement

Tests

• Parser unit test: DESC ecommerce parses as DescribeTable("ecommerce")
• Parser unit test: DESC TABLE ecommerce still parses as DescribeTable("ecommerce")
• Parser unit test: DESC PIPELINE mypipe still parses as DescribePipeline("mypipe")
• Parser unit test: DESC MATERIALIZED VIEW myview still parses as DescribeMaterializedView("myview")