Fix #1249 Left joins in SQLite can break the query macros (#1789)

* Reproduce github issue#1249: Left joins in sqlite can break the query macros

* Fix panic caused by unknown cursor columns when executing NullRow command. Fixes #1249

sqlx-core/src/sqlite/connection/explain.rs

@@ -97,6 +97,50 @@ fn opcode_to_type(op: &str) -> DataType {
     }
 }
 
+fn root_block_columns(
+    conn: &mut ConnectionState,
+) -> Result<HashMap<i64, HashMap<i64, DataType>>, Error> {
+    let table_block_columns: Vec<(i64, i64, String)> = execute::iter(
+        conn,
+        "SELECT s.rootpage, col.cid as colnum, col.type
+         FROM sqlite_schema s
+         JOIN pragma_table_info(s.name) AS col
+         WHERE s.type = 'table'",
+        None,
+        false,
+    )?
+    .filter_map(|res| res.map(|either| either.right()).transpose())
+    .map(|row| FromRow::from_row(&row?))
+    .collect::<Result<Vec<_>, Error>>()?;
+
+    let index_block_columns: Vec<(i64, i64, String)> = execute::iter(
+        conn,
+        "SELECT s.rootpage, idx.seqno as colnum, col.type
+         FROM sqlite_schema s
+         JOIN pragma_index_info(s.name) AS idx
+         LEFT JOIN pragma_table_info(s.tbl_name) as col
+           ON col.cid = idx.cid
+           WHERE s.type = 'index'",
+        None,
+        false,
+    )?
+    .filter_map(|res| res.map(|either| either.right()).transpose())
+    .map(|row| FromRow::from_row(&row?))
+    .collect::<Result<Vec<_>, Error>>()?;
+
+    let mut row_info: HashMap<i64, HashMap<i64, DataType>> = HashMap::new();
+    for (block, colnum, datatype) in table_block_columns {
+        let row_info = row_info.entry(block).or_default();
+        row_info.insert(colnum, datatype.parse().unwrap_or(DataType::Null));
+    }
+    for (block, colnum, datatype) in index_block_columns {
+        let row_info = row_info.entry(block).or_default();
+        row_info.insert(colnum, datatype.parse().unwrap_or(DataType::Null));
+    }
+
+    return Ok(row_info);
+}
+
 // Opcode Reference: https://sqlite.org/opcode.html
 pub(super) fn explain(
     conn: &mut ConnectionState,
@@ -112,6 +156,8 @@ pub(super) fn explain(
     // Nullable columns
     let mut n = HashMap::<i64, bool>::with_capacity(6);
 
+    let root_block_cols = root_block_columns(conn)?;
+
     let program: Vec<(i64, String, i64, i64, i64, Vec<u8>)> =
         execute::iter(conn, &format!("EXPLAIN {}", query), None, false)?
             .filter_map(|res| res.map(|either| either.right()).transpose())
@@ -190,7 +236,23 @@ pub(super) fn explain(
 
             OP_OPEN_READ | OP_OPEN_WRITE | OP_OPEN_EPHEMERAL | OP_OPEN_AUTOINDEX => {
                 //Create a new pointer which is referenced by p1
-                p.insert(p1, HashMap::with_capacity(6));
+
+                //Create a new pointer which is referenced by p1, take column metadata from db schema if found
+                if p3 == 0 {
+                    if let Some(columns) = root_block_cols.get(&p2) {
+                        p.insert(
+                            p1,
+                            columns
+                                .iter()
+                                .map(|(&colnum, &datatype)| (colnum, datatype))
+                                .collect(),
+                        );
+                    } else {
+                        p.insert(p1, HashMap::with_capacity(6));
+                    }
+                } else {
+                    p.insert(p1, HashMap::with_capacity(6));
+                }
             }
 
             OP_VARIABLE => {
@@ -339,3 +401,126 @@ pub(super) fn explain(
 
     Ok((output, nullable))
 }
+
+#[test]
+fn test_root_block_columns_has_types() {
+    use crate::sqlite::SqliteConnectOptions;
+    use std::str::FromStr;
+    let conn_options = SqliteConnectOptions::from_str("sqlite::memory:").unwrap();
+    let mut conn = super::EstablishParams::from_options(&conn_options)
+        .unwrap()
+        .establish()
+        .unwrap();
+
+    assert!(execute::iter(
+        &mut conn,
+        r"CREATE TABLE t(a INTEGER PRIMARY KEY, b_null TEXT NULL, b TEXT NOT NULL);",
+        None,
+        false
+    )
+    .unwrap()
+    .next()
+    .is_some());
+    assert!(
+        execute::iter(&mut conn, r"CREATE INDEX i1 on t (a,b_null);", None, false)
+            .unwrap()
+            .next()
+            .is_some()
+    );
+    assert!(execute::iter(
+        &mut conn,
+        r"CREATE UNIQUE INDEX i2 on t (a,b_null);",
+        None,
+        false
+    )
+    .unwrap()
+    .next()
+    .is_some());
+    assert!(execute::iter(
+        &mut conn,
+        r"CREATE TABLE t2(a INTEGER, b_null NUMERIC NULL, b NUMERIC NOT NULL);",
+        None,
+        false
+    )
+    .unwrap()
+    .next()
+    .is_some());
+    assert!(execute::iter(
+        &mut conn,
+        r"CREATE INDEX t2i1 on t2 (a,b_null);",
+        None,
+        false
+    )
+    .unwrap()
+    .next()
+    .is_some());
+    assert!(execute::iter(
+        &mut conn,
+        r"CREATE UNIQUE INDEX t2i2 on t2 (a,b);",
+        None,
+        false
+    )
+    .unwrap()
+    .next()
+    .is_some());
+
+    let table_block_nums: HashMap<String, i64> = execute::iter(
+        &mut conn,
+        r"select name, rootpage from sqlite_master",
+        None,
+        false,
+    )
+    .unwrap()
+    .filter_map(|res| res.map(|either| either.right()).transpose())
+    .map(|row| FromRow::from_row(row.as_ref().unwrap()))
+    .collect::<Result<HashMap<_, _>, Error>>()
+    .unwrap();
+
+    let root_block_cols = root_block_columns(&mut conn).unwrap();
+
+    assert_eq!(6, root_block_cols.len());
+
+    //prove that we have some information for each table & index
+    for blocknum in table_block_nums.values() {
+        assert!(root_block_cols.contains_key(blocknum));
+    }
+
+    //prove that each block has the correct information
+    {
+        let blocknum = table_block_nums["t"];
+        assert_eq!((DataType::Int64), root_block_cols[&blocknum][&0]);
+        assert_eq!((DataType::Text), root_block_cols[&blocknum][&1]);
+        assert_eq!((DataType::Text), root_block_cols[&blocknum][&2]);
+    }
+
+    {
+        let blocknum = table_block_nums["i1"];
+        assert_eq!((DataType::Int64), root_block_cols[&blocknum][&0]);
+        assert_eq!((DataType::Text), root_block_cols[&blocknum][&1]);
+    }
+
+    {
+        let blocknum = table_block_nums["i2"];
+        assert_eq!((DataType::Int64), root_block_cols[&blocknum][&0]);
+        assert_eq!((DataType::Text), root_block_cols[&blocknum][&1]);
+    }
+
+    {
+        let blocknum = table_block_nums["t2"];
+        assert_eq!((DataType::Int64), root_block_cols[&blocknum][&0]);
+        assert_eq!((DataType::Null), root_block_cols[&blocknum][&1]);
+        assert_eq!((DataType::Null), root_block_cols[&blocknum][&2]);
+    }
+
+    {
+        let blocknum = table_block_nums["t2i1"];
+        assert_eq!((DataType::Int64), root_block_cols[&blocknum][&0]);
+        assert_eq!((DataType::Null), root_block_cols[&blocknum][&1]);
+    }
+
+    {
+        let blocknum = table_block_nums["t2i2"];
+        assert_eq!((DataType::Int64), root_block_cols[&blocknum][&0]);
+        assert_eq!((DataType::Null), root_block_cols[&blocknum][&1]);
+    }
+}

tests/sqlite/describe.rs

@@ -242,5 +242,17 @@ async fn it_describes_left_join() -> anyhow::Result<()> {
     assert_eq!(d.column(1).type_info().name(), "INTEGER");
     assert_eq!(d.nullable(1), Some(false));
 
+    let d = conn
+        .describe(
+            "select tweet.id, accounts.id from accounts left join tweet on tweet.id = accounts.id",
+        )
+        .await?;
+
+    assert_eq!(d.column(0).type_info().name(), "INTEGER");
+    assert_eq!(d.nullable(0), Some(true));
+
+    assert_eq!(d.column(1).type_info().name(), "INTEGER");
+    assert_eq!(d.nullable(1), Some(false));
+
     Ok(())
 }