fix: only require DESCRIBE TABLE for Snowflake and ClickHouse dialect (apache#1386)

Author: alamb

src/dialect/clickhouse.rs

@@ -33,4 +33,8 @@ impl Dialect for ClickHouseDialect {
     fn supports_select_wildcard_except(&self) -> bool {
         true
     }
+
+    fn describe_requires_table_keyword(&self) -> bool {
+        true
+    }
 }

src/dialect/mod.rs

@@ -485,9 +485,20 @@ pub trait Dialect: Debug + Any {
         }
     }
 
+    /// Returns the precedence when the precedence is otherwise unknown
     fn prec_unknown(&self) -> u8 {
         0
     }
+
+    /// Returns true if this dialect requires the `TABLE` keyword after `DESCRIBE`
+    ///
+    /// Defaults to false.
+    ///
+    /// If true, the following statement is valid: `DESCRIBE TABLE my_table`
+    /// If false, the following statements are valid: `DESCRIBE my_table` and `DESCRIBE table`
+    fn describe_requires_table_keyword(&self) -> bool {
+        false
+    }
 }
 
 /// This represents the operators for which precedence must be defined

src/dialect/snowflake.rs

@@ -154,6 +154,10 @@ impl Dialect for SnowflakeDialect {
             _ => None,
         }
     }
+
+    fn describe_requires_table_keyword(&self) -> bool {
+        true
+    }
 }
 
 /// Parse snowflake create table statement.

src/parser/mod.rs

@@ -8185,15 +8185,20 @@ impl<'a> Parser<'a> {
                 format,
             }),
             _ => {
-                let mut hive_format = None;
-                match self.parse_one_of_keywords(&[Keyword::EXTENDED, Keyword::FORMATTED]) {
-                    Some(Keyword::EXTENDED) => hive_format = Some(HiveDescribeFormat::Extended),
-                    Some(Keyword::FORMATTED) => hive_format = Some(HiveDescribeFormat::Formatted),
-                    _ => {}
-                }
+                let hive_format =
+                    match self.parse_one_of_keywords(&[Keyword::EXTENDED, Keyword::FORMATTED]) {
+                        Some(Keyword::EXTENDED) => Some(HiveDescribeFormat::Extended),
+                        Some(Keyword::FORMATTED) => Some(HiveDescribeFormat::Formatted),
+                        _ => None,
+                    };
+
+                let has_table_keyword = if self.dialect.describe_requires_table_keyword() {
+                    // only allow to use TABLE keyword for DESC|DESCRIBE statement
+                    self.parse_keyword(Keyword::TABLE)
+                } else {
+                    false
+                };
 
-                // only allow to use TABLE keyword for DESC|DESCRIBE statement
-                let has_table_keyword = self.parse_keyword(Keyword::TABLE);
                 let table_name = self.parse_object_name(false)?;
                 Ok(Statement::ExplainTable {
                     describe_alias,

tests/sqlparser_clickhouse.rs

@@ -1376,6 +1376,36 @@ fn parse_select_table_function_settings() {
     }
 }
 
+#[test]
+fn explain_describe() {
+    clickhouse().verified_stmt("DESCRIBE test.table");
+    clickhouse().verified_stmt("DESCRIBE TABLE test.table");
+}
+
+#[test]
+fn explain_desc() {
+    clickhouse().verified_stmt("DESC test.table");
+    clickhouse().verified_stmt("DESC TABLE test.table");
+}
+
+#[test]
+fn parse_explain_table() {
+    match clickhouse().verified_stmt("EXPLAIN TABLE test_identifier") {
+        Statement::ExplainTable {
+            describe_alias,
+            hive_format,
+            has_table_keyword,
+            table_name,
+        } => {
+            pretty_assertions::assert_eq!(describe_alias, DescribeAlias::Explain);
+            pretty_assertions::assert_eq!(hive_format, None);
+            pretty_assertions::assert_eq!(has_table_keyword, true);
+            pretty_assertions::assert_eq!("test_identifier", table_name.to_string());
+        }
+        _ => panic!("Unexpected Statement, must be ExplainTable"),
+    }
+}
+
 fn clickhouse() -> TestedDialects {
     TestedDialects {
         dialects: vec![Box::new(ClickHouseDialect {})],

tests/sqlparser_common.rs

@@ -4301,29 +4301,16 @@ fn parse_explain_table() {
     validate_explain("EXPLAIN test_identifier", DescribeAlias::Explain, false);
     validate_explain("DESCRIBE test_identifier", DescribeAlias::Describe, false);
     validate_explain("DESC test_identifier", DescribeAlias::Desc, false);
-    validate_explain(
-        "EXPLAIN TABLE test_identifier",
-        DescribeAlias::Explain,
-        true,
-    );
-    validate_explain(
-        "DESCRIBE TABLE test_identifier",
-        DescribeAlias::Describe,
-        true,
-    );
-    validate_explain("DESC TABLE test_identifier", DescribeAlias::Desc, true);
 }
 
 #[test]
 fn explain_describe() {
     verified_stmt("DESCRIBE test.table");
-    verified_stmt("DESCRIBE TABLE test.table");
 }
 
 #[test]
 fn explain_desc() {
     verified_stmt("DESC test.table");
-    verified_stmt("DESC TABLE test.table");
 }
 
 #[test]

tests/sqlparser_hive.rs

@@ -21,7 +21,7 @@ use sqlparser::ast::{
     UnaryOperator, Value,
 };
 use sqlparser::dialect::{GenericDialect, HiveDialect, MsSqlDialect};
-use sqlparser::parser::{ParserError, ParserOptions};
+use sqlparser::parser::ParserError;
 use sqlparser::test_utils::*;
 
 #[test]
@@ -35,18 +35,11 @@ fn parse_table_create() {
     hive().verified_stmt(serdeproperties);
 }
 
-fn generic(options: Option<ParserOptions>) -> TestedDialects {
-    TestedDialects {
-        dialects: vec![Box::new(GenericDialect {})],
-        options,
-    }
-}
-
 #[test]
 fn parse_describe() {
-    let describe = r#"DESCRIBE namespace.`table`"#;
-    hive().verified_stmt(describe);
-    generic(None).verified_stmt(describe);
+    hive_and_generic().verified_stmt(r#"DESCRIBE namespace.`table`"#);
+    hive_and_generic().verified_stmt(r#"DESCRIBE namespace.table"#);
+    hive_and_generic().verified_stmt(r#"DESCRIBE table"#);
 }
 
 #[test]
@@ -414,3 +407,10 @@ fn hive() -> TestedDialects {
         options: None,
     }
 }
+
+fn hive_and_generic() -> TestedDialects {
+    TestedDialects {
+        dialects: vec![Box::new(HiveDialect {}), Box::new(GenericDialect {})],
+        options: None,
+    }
+}

tests/sqlparser_snowflake.rs

@@ -2292,3 +2292,33 @@ fn test_parse_position() {
     snowflake().verified_query("SELECT position('an', 'banana', 1)");
     snowflake().verified_query("SELECT n, h, POSITION(n IN h) FROM pos");
 }
+
+#[test]
+fn explain_describe() {
+    snowflake().verified_stmt("DESCRIBE test.table");
+    snowflake().verified_stmt("DESCRIBE TABLE test.table");
+}
+
+#[test]
+fn explain_desc() {
+    snowflake().verified_stmt("DESC test.table");
+    snowflake().verified_stmt("DESC TABLE test.table");
+}
+
+#[test]
+fn parse_explain_table() {
+    match snowflake().verified_stmt("EXPLAIN TABLE test_identifier") {
+        Statement::ExplainTable {
+            describe_alias,
+            hive_format,
+            has_table_keyword,
+            table_name,
+        } => {
+            assert_eq!(describe_alias, DescribeAlias::Explain);
+            assert_eq!(hive_format, None);
+            assert_eq!(has_table_keyword, true);
+            assert_eq!("test_identifier", table_name.to_string());
+        }
+        _ => panic!("Unexpected Statement, must be ExplainTable"),
+    }
+}