[SOLVED] DESCRIBE TABLE see which columns are NOT NULL

DESCRIBE TABLE see which columns are NOT NULL

In Apache Spark SQL (Azure Databricks), I created a table like this:

CREATE TABLE t(
    a BIGINT,
    b BIGINT NOT NULL
)

I have verified that I have one nullable column and one non-nullable column, as I get an error if I try to insert NULL in column b but I can insert null in column a.

However, the following statement

DESCRIBE TABLE t

does not tell me which columns are nullable and which are not null. Neither does DESCRIBE TABLE EXTENDED. How can I get the full description?

Solution

Spark SQL auxiliary commands like DESCRIBE TABLE and SHOW COLUMNS do not display column NULL constraints as per the docs.

There is this command:

SHOW TABLE EXTENDED like 't'

which returns the schema in the information column along with others information but not much readable.

//Table Properties: [transient_lastDdlTime=1643396075]
//.....
//Partition Provider: Catalog
//Schema: root
// |-- a: long (nullable = true)
// |-- b: long (nullable = false)

But if you can use spark.catalog with scala/python api then this is simple:

spark.catalog.listColumns("t").show()
//+----+-----------+--------+--------+-----------+--------+
//|name|description|dataType|nullable|isPartition|isBucket|
//+----+-----------+--------+--------+-----------+--------+
//|   a|       null|  bigint|    true|      false|   false|
//|   b|       null|  bigint|   false|      false|   false|
//+----+-----------+--------+--------+-----------+--------+