LiuYuHui opened a new pull request, #2642:
URL: https://github.com/apache/arrow-datafusion/pull/2642
# Which issue does this PR close?
Closes #2606.
# Rationale for this change
# What changes are included in this PR?
When the user executes the `DESCRIBE <table>`, the output will be the following.
```sql
❯ create table foo as select * from (values (1), (3), (2), (10), (8));
+---------+
| column1 |
+---------+
| 1 |
| 3 |
| 2 |
| 10 |
| 8 |
+---------+
5 rows in set. Query took 0.013 seconds.
❯ describe foo;
+-------------+-----------+-------------+
| column_name | data_type | is_nullable |
+-------------+-----------+-------------+
| column1 | Int64 | YES |
+-------------+-----------+-------------+
1 row in set. Query took 0.016 seconds.
```
# Are there any user-facing changes?
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# Does this PR break compatibility with Ballista?
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[GitHub] [arrow-datafusion] andygrove commented on a diff in pull request #2642: Implement DESCRIBE
Posted by GitBox <gi...@apache.org>.
andygrove commented on code in PR #2642:
URL: https://github.com/apache/arrow-datafusion/pull/2642#discussion_r884315275
##########
datafusion/sql/src/planner.rs:
##########
@@ -139,6 +139,7 @@ impl<'a, S: ContextProvider> SqlToRel<'a, S> {
match statement {
DFStatement::CreateExternalTable(s) => self.external_table_to_plan(s),
DFStatement::Statement(s) => self.sql_statement_to_plan(*s),
+ DFStatement::DescribeTable(s) => self.decrible_table_to_plan(s),
Review Comment:
```suggestion
DFStatement::DescribeTable(s) => self.describe_table_to_plan(s),
```
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[GitHub] [arrow-datafusion] LiuYuHui commented on pull request #2642: Implement DESCRIBE
Posted by GitBox <gi...@apache.org>.
LiuYuHui commented on PR #2642:
URL: https://github.com/apache/arrow-datafusion/pull/2642#issuecomment-1141836387
@alamb, I have fixed the nonexistent table case and added the test, please take a look.
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[GitHub] [arrow-datafusion] alamb commented on pull request #2642: Implement DESCRIBE
Posted by GitBox <gi...@apache.org>.
alamb commented on PR #2642:
URL: https://github.com/apache/arrow-datafusion/pull/2642#issuecomment-1141107090
> Hi @alamb, thanks for your review, currently this PR only implements describe table_name, the describe table table_name is not implemented, this is why your test case has an error, should I also implement the describe table table_name?
🤦 -- no sorry @LiuYuHui I was mistaken on the syntax of `describe` -- no need to implement `describe table foo`
I tried the correct syntax and it works great 👍
```sql
❯ describe y;
+-------------+-----------+-------------+
| column_name | data_type | is_nullable |
+-------------+-----------+-------------+
| column1 | Int64 | YES |
| column2 | Int64 | YES |
+-------------+-----------+-------------+
2 rows in set. Query took 0.006 seconds.
```
However, I do think this PR needs a test.
Also, would it be possible to generate an error if the table didn't exist?
For example, mysql does the following for a non existent table:
```sql
mysql> describe ff;
ERROR 1146 (42S02): Table 'foo.ff' doesn't exist
```
But this PR returns an empty row:
```sql
❯ describe table;
0 rows in set. Query took 0.020 seconds.
```
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[GitHub] [arrow-datafusion] andygrove commented on a diff in pull request #2642: Implement DESCRIBE
Posted by GitBox <gi...@apache.org>.
andygrove commented on code in PR #2642:
URL: https://github.com/apache/arrow-datafusion/pull/2642#discussion_r884315197
##########
datafusion/sql/src/planner.rs:
##########
@@ -353,6 +354,24 @@ impl<'a, S: ContextProvider> SqlToRel<'a, S> {
}
}
+ pub fn decrible_table_to_plan(
+ &self,
+ statement: DescribeTable,
+ ) -> Result<LogicalPlan> {
+ if self.has_table("information_schema", "tables") {
+ let table_name = statement.table_name;
+ let sql = format!("SELECT column_name, data_type, is_nullable \
+ FROM information_schema.columns WHERE table_name = '{table_name}';");
+ let mut rewrite = DFParser::parse_sql(&sql[..])?;
+ self.statement_to_plan(rewrite.pop_front().unwrap())
+ } else {
+ Err(DataFusionError::Plan(
+ "SHOW TABLES is not supported unless information_schema is enabled"
Review Comment:
```suggestion
"DESCRIBE TABLE is not supported unless information_schema is enabled"
```
##########
datafusion/sql/src/planner.rs:
##########
@@ -353,6 +354,24 @@ impl<'a, S: ContextProvider> SqlToRel<'a, S> {
}
}
+ pub fn decrible_table_to_plan(
Review Comment:
```suggestion
pub fn decribe_table_to_plan(
```
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[GitHub] [arrow-datafusion] andygrove commented on a diff in pull request #2642: Implement DESCRIBE
Posted by GitBox <gi...@apache.org>.
andygrove commented on code in PR #2642:
URL: https://github.com/apache/arrow-datafusion/pull/2642#discussion_r884315207
##########
datafusion/sql/src/planner.rs:
##########
@@ -353,6 +354,24 @@ impl<'a, S: ContextProvider> SqlToRel<'a, S> {
}
}
+ pub fn decrible_table_to_plan(
Review Comment:
```suggestion
pub fn describe_table_to_plan(
```
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[GitHub] [arrow-datafusion] LiuYuHui commented on pull request #2642: Implement DESCRIBE
Posted by GitBox <gi...@apache.org>.
LiuYuHui commented on PR #2642:
URL: https://github.com/apache/arrow-datafusion/pull/2642#issuecomment-1141021530
Hi @alamb, thanks for your review, currently this PR only implements `describe table_name`, the `describe table table_name` is not implemented, this is why your test case has an error, should I also implement the `describe table table_name`?
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[GitHub] [arrow-datafusion] alamb merged pull request #2642: Implement DESCRIBE
Posted by GitBox <gi...@apache.org>.
alamb merged PR #2642:
URL: https://github.com/apache/arrow-datafusion/pull/2642
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