Fix some places where trying to parse an empty string could panic.

crates/sql-parser/src/parser/errors.rs

@@ -62,6 +62,8 @@ pub enum SqlUnsupported {
     MultiStatement,
     #[error("Multi-table DELETE is not supported")]
     MultiTableDelete,
+    #[error("Empty SQL query")]
+    Empty,
 }
 
 impl SqlUnsupported {

crates/sql-parser/src/parser/sql.rs

@@ -154,6 +154,9 @@ pub fn parse_sql(sql: &str) -> SqlParseResult<SqlAst> {
     if stmts.len() > 1 {
         return Err(SqlUnsupported::MultiStatement.into());
     }
+    if stmts.is_empty() {
+        return Err(SqlUnsupported::Empty.into());
+    }
     parse_statement(stmts.swap_remove(0))
 }
 
@@ -519,6 +522,9 @@ mod tests {
             "select a from t where",
             // Empty GROUP BY
             "select a, count(*) from t group by",
+            // Empty statement
+            "",
+            " ",
         ] {
             assert!(parse_sql(sql).is_err());
         }

crates/sql-parser/src/parser/sub.rs

@@ -69,10 +69,11 @@ use super::{
 /// Parse a SQL string
 pub fn parse_subscription(sql: &str) -> SqlParseResult<SqlAst> {
     let mut stmts = Parser::parse_sql(&PostgreSqlDialect {}, sql)?;
-    if stmts.len() > 1 {
-        return Err(SqlUnsupported::MultiStatement.into());
+    match stmts.len() {
+        0 => Err(SqlUnsupported::Empty.into()),
+        1 => parse_statement(stmts.swap_remove(0)),
+        _ => Err(SqlUnsupported::MultiStatement.into()),
     }
-    parse_statement(stmts.swap_remove(0))
 }
 
 /// Parse a SQL query
@@ -174,6 +175,8 @@ mod tests {
     fn unsupported() {
         for sql in [
             "delete from t",
+            " ",
+            "",
             "select distinct a from t",
             "select * from (select * from t) join (select * from s) on a = b",
         ] {