## What changes were proposed in this pull request?
This pr updated parsing rules in `SqlBase.g4` to support a SQL query below when ANSI mode enabled;
```
SELECT CAST('2017-08-04' AS DATE) + 1 days;
```
The current master cannot parse it though, other dbms-like systems support the syntax (e.g., hive and mysql). Also, the syntax is frequently used in the official TPC-DS queries.
This pr added new tokens as follows;
```
YEAR | YEARS | MONTH | MONTHS | WEEK | WEEKS | DAY | DAYS | HOUR | HOURS | MINUTE
MINUTES | SECOND | SECONDS | MILLISECOND | MILLISECONDS | MICROSECOND | MICROSECONDS
```
Then, it registered the keywords below as the ANSI reserved (this follows SQL-2011);
```
DAY | HOUR | MINUTE | MONTH | SECOND | YEAR
```
## How was this patch tested?
Added tests in `SQLQuerySuite`, `ExpressionParserSuite`, and `TableIdentifierParserSuite`.
Closes#20433 from maropu/SPARK-23264.
Authored-by: Takeshi Yamamuro <yamamuro@apache.org>
Signed-off-by: Takeshi Yamamuro <yamamuro@apache.org>
## What changes were proposed in this pull request?
Currently we can use `df.printSchema` to discover the schema information for a query. We should have a way to describe the output schema of a query using SQL interface.
Example:
DESCRIBE SELECT * FROM desc_table
DESCRIBE QUERY SELECT * FROM desc_table
```SQL
spark-sql> create table desc_table (c1 int comment 'c1-comment', c2 decimal comment 'c2-comment', c3 string);
spark-sql> desc select * from desc_table;
c1 int c1-comment
c2 decimal(10,0) c2-comment
c3 string NULL
```
## How was this patch tested?
Added a new test under SQLQueryTestSuite and SparkSqlParserSuite
Closes#23883 from dilipbiswal/dkb_describe_query.
Authored-by: Dilip Biswal <dbiswal@us.ibm.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>
## What changes were proposed in this pull request?
This pr targeted to define reserved/non-reserved keywords for Spark SQL based on the ANSI SQL standards and the other database-like systems (e.g., PostgreSQL). We assume that they basically follow the ANSI SQL-2011 standard, but it is slightly different between each other. Therefore, this pr documented all the keywords in `docs/sql-reserved-and-non-reserved-key-words.md`.
NOTE: This pr only added a small set of keywords as reserved ones and these keywords are reserved in all the ANSI SQL standards (SQL-92, SQL-99, SQL-2003, SQL-2008, SQL-2011, and SQL-2016) and PostgreSQL. This is because there is room to discuss which keyword should be reserved or not, .e.g., interval units (day, hour, minute, second, ...) are reserved in the ANSI SQL standards though, they are not reserved in PostgreSQL. Therefore, we need more researches about the other database-like systems (e.g., Oracle Databases, DB2, SQL server) in follow-up activities.
References:
- The reserved/non-reserved SQL keywords in the ANSI SQL standards: https://developer.mimer.com/wp-content/uploads/2018/05/Standard-SQL-Reserved-Words-Summary.pdf
- SQL Key Words in PostgreSQL: https://www.postgresql.org/docs/current/sql-keywords-appendix.html
## How was this patch tested?
Added tests in `TableIdentifierParserSuite`.
Closes#23259 from maropu/SPARK-26215-WIP.
Authored-by: Takeshi Yamamuro <yamamuro@apache.org>
Signed-off-by: Takeshi Yamamuro <yamamuro@apache.org>
