ShowColumns Unary Command¶
ShowColumns is a UnaryCommand (and a Logical Command) that represents SHOW COLUMNS SQL statement in logical query plans.
Creating Instance¶
ShowColumns takes the following to be created:
- Child Logical Operator
- Namespace
- Output Schema
ShowColumns is created when:
AstBuilderis requested to parse SHOW COLUMNS statement
Output Schema¶
ShowColumns can be given output Attributes when created.
The output schema is by default as follows:
| Column Name | Data Type | Nullable |
|---|---|---|
col_name | StringType | ❌ |
Logical Analysis¶
ShowColumns is resolved to ShowColumnsCommand logical runnable command by ResolveSessionCatalog logical resolution rule.
Query Planning¶
DataSourceV2Strategy throws an AnalysisException for ShowColumnss in query plans.