feat: Support DESCRIBE table_name (#340)

* feat: Support DESCRIBE

* feat: Support DESCRIBE table_name

* Update src/ast/mod.rs

Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>

* Update src/ast/mod.rs

Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>

* Update src/ast/mod.rs

Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>

Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>

src/ast/mod.rs

@@ -764,8 +764,18 @@ pub enum Statement {
         data_types: Vec<DataType>,
         statement: Box<Statement>,
     },
-    /// EXPLAIN
+    /// EXPLAIN TABLE
+    /// Note: this is a MySQL-specific statement. See <https://dev.mysql.com/doc/refman/8.0/en/explain.html>
+    ExplainTable {
+        // If true, query used the MySQL `DESCRIBE` alias for explain
+        describe_alias: bool,
+        // Table name
+        table_name: ObjectName,
+    },
+    /// EXPLAIN / DESCRIBE for select_statement
     Explain {
+        // If true, query used the MySQL `DESCRIBE` alias for explain
+        describe_alias: bool,
         /// Carry out the command and show actual run times and other statistics.
         analyze: bool,
         // Display additional information regarding the plan.
@@ -781,12 +791,29 @@ impl fmt::Display for Statement {
     #[allow(clippy::cognitive_complexity)]
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self {
+            Statement::ExplainTable {
+                describe_alias,
+                table_name,
+            } => {
+                if *describe_alias {
+                    write!(f, "DESCRIBE ")?;
+                } else {
+                    write!(f, "EXPLAIN ")?;
+                }
+
+                write!(f, "{}", table_name)
+            }
             Statement::Explain {
+                describe_alias,
                 verbose,
                 analyze,
                 statement,
             } => {
-                write!(f, "EXPLAIN ")?;
+                if *describe_alias {
+                    write!(f, "DESCRIBE ")?;
+                } else {
+                    write!(f, "EXPLAIN ")?;
+                }
 
                 if *analyze {
                     write!(f, "ANALYZE ")?;

src/parser.rs

@@ -141,7 +141,8 @@ impl<'a> Parser<'a> {
     pub fn parse_statement(&mut self) -> Result<Statement, ParserError> {
         match self.next_token() {
             Token::Word(w) => match w.keyword {
-                Keyword::EXPLAIN => Ok(self.parse_explain()?),
+                Keyword::DESCRIBE => Ok(self.parse_explain(true)?),
+                Keyword::EXPLAIN => Ok(self.parse_explain(false)?),
                 Keyword::ANALYZE => Ok(self.parse_analyze()?),
                 Keyword::SELECT | Keyword::WITH | Keyword::VALUES => {
                     self.prev_token();
@@ -2218,17 +2219,25 @@ impl<'a> Parser<'a> {
         })
     }
 
-    pub fn parse_explain(&mut self) -> Result<Statement, ParserError> {
+    pub fn parse_explain(&mut self, describe_alias: bool) -> Result<Statement, ParserError> {
         let analyze = self.parse_keyword(Keyword::ANALYZE);
         let verbose = self.parse_keyword(Keyword::VERBOSE);
 
-        let statement = Box::new(self.parse_statement()?);
+        if let Some(statement) = self.maybe_parse(|parser| parser.parse_statement()) {
+            Ok(Statement::Explain {
+                describe_alias,
+                analyze,
+                verbose,
+                statement: Box::new(statement),
+            })
+        } else {
+            let table_name = self.parse_object_name()?;
 
-        Ok(Statement::Explain {
-            analyze,
-            verbose,
-            statement,
-        })
+            Ok(Statement::ExplainTable {
+                describe_alias,
+                table_name,
+            })
+        }
     }
 
     /// Parse a query expression, i.e. a `SELECT` statement optionally

tests/sqlparser_common.rs

@@ -1803,6 +1803,7 @@ fn parse_scalar_function_in_projection() {
 fn run_explain_analyze(query: &str, expected_verbose: bool, expected_analyze: bool) {
     match verified_stmt(query) {
         Statement::Explain {
+            describe_alias: _,
             analyze,
             verbose,
             statement,
@@ -1815,8 +1816,28 @@ fn run_explain_analyze(query: &str, expected_verbose: bool, expected_analyze: bo
     }
 }
 
+#[test]
+fn parse_explain_table() {
+    let validate_explain = |query: &str, expected_describe_alias: bool| match verified_stmt(query) {
+        Statement::ExplainTable {
+            describe_alias,
+            table_name,
+        } => {
+            assert_eq!(describe_alias, expected_describe_alias);
+            assert_eq!("test_identifier", table_name.to_string());
+        }
+        _ => panic!("Unexpected Statement, must be ExplainTable"),
+    };
+
+    validate_explain("EXPLAIN test_identifier", false);
+    validate_explain("DESCRIBE test_identifier", true);
+}
+
 #[test]
 fn parse_explain_analyze_with_simple_select() {
+    // Describe is an alias for EXPLAIN
+    run_explain_analyze("DESCRIBE SELECT sqrt(id) FROM foo", false, false);
+
     run_explain_analyze("EXPLAIN SELECT sqrt(id) FROM foo", false, false);
     run_explain_analyze("EXPLAIN VERBOSE SELECT sqrt(id) FROM foo", true, false);
     run_explain_analyze("EXPLAIN ANALYZE SELECT sqrt(id) FROM foo", false, true);