Merge pull request #7829 from planetscale/vtexplain-lj

VTExplain: Add support for multi table join query

go/vt/vtexplain/testdata/multi-output/selectsharded-output.txt

@@ -172,3 +172,15 @@ select id from user where not id in (select col from music where music.user_id =
 2 ks_sharded/40-80: select col from music where music.user_id = 411 limit 10001
 
 ----------------------------------------------------------------------
+SELECT user.id, user.name, name_info.info FROM user INNER JOIN music ON (user.id = music.user_id) LEFT OUTER JOIN name_info ON (user.name = name_info.name)
+
+1 ks_sharded/-40: select `user`.id, `user`.`name` from `user` join music on `user`.id = music.user_id limit 10001
+1 ks_sharded/40-80: select `user`.id, `user`.`name` from `user` join music on `user`.id = music.user_id limit 10001
+1 ks_sharded/80-c0: select `user`.id, `user`.`name` from `user` join music on `user`.id = music.user_id limit 10001
+1 ks_sharded/c0-: select `user`.id, `user`.`name` from `user` join music on `user`.id = music.user_id limit 10001
+2 ks_sharded/40-80: select name_info.info from name_info where name_info.`name` = 'name_val_2' limit 10001
+3 ks_sharded/40-80: select name_info.info from name_info where name_info.`name` = 'name_val_2' limit 10001
+4 ks_sharded/40-80: select name_info.info from name_info where name_info.`name` = 'name_val_2' limit 10001
+5 ks_sharded/40-80: select name_info.info from name_info where name_info.`name` = 'name_val_2' limit 10001
+
+----------------------------------------------------------------------

go/vt/vtexplain/testdata/selectsharded-queries.sql

@@ -34,3 +34,5 @@ select id, case when substr(name, 1, 5) = 'alice' then 'ALICE' when name = 'bob'
 select id, 'abc' as test from user where id = 1 union all select id, 'def' as test from user where id = 1 union all select id, 'ghi' as test from user where id = 1 /* union all */;
 
 select id from user where not id in (select col from music where music.user_id = 42) and id in (select col from music where music.user_id = 411);
+
+SELECT user.id, user.name, name_info.info FROM user INNER JOIN music ON (user.id = music.user_id) LEFT OUTER JOIN name_info ON (user.name = name_info.name);

go/vt/vtexplain/vtexplain_vttablet.go

@@ -482,23 +482,25 @@ func (t *explainTablet) HandleQuery(c *mysql.Conn, query string, callback func(*
 			return fmt.Errorf("unsupported select with multiple from clauses")
 		}
 
-		var table sqlparser.TableIdent
-		switch node := selStmt.From[0].(type) {
-		case *sqlparser.AliasedTableExpr:
-			table = sqlparser.GetTableName(node.Expr)
-		}
+		tables := getTables(selStmt.From[0])
+		colTypeMap := map[string]querypb.Type{}
+		for _, table := range tables {
+			tableName := sqlparser.String(table)
+			columns, exists := tableColumns[tableName]
+			if !exists && tableName != "" && tableName != "dual" {
+				return fmt.Errorf("unable to resolve table name %s", tableName)
+			}
 
-		// For complex select queries just return an empty result
-		// since it's too hard to figure out the real columns
-		if table.IsEmpty() {
-			log.V(100).Infof("query %s result {}\n", query)
-			return callback(&sqltypes.Result{})
-		}
+			for k, v := range columns {
+				if colType, exists := colTypeMap[k]; exists {
+					if colType != v {
+						return fmt.Errorf("column type mismatch for column : %s, types: %d vs %d", k, colType, v)
+					}
+					continue
+				}
+				colTypeMap[k] = v
+			}
 
-		tableName := sqlparser.String(table)
-		colTypeMap := tableColumns[tableName]
-		if colTypeMap == nil && tableName != "dual" {
-			return fmt.Errorf("unable to resolve table name %s", tableName)
 		}
 
 		colNames := make([]string, 0, 4)
@@ -593,6 +595,18 @@ func (t *explainTablet) HandleQuery(c *mysql.Conn, query string, callback func(*
 	return callback(result)
 }
 
+func getTables(node sqlparser.SQLNode) []sqlparser.TableIdent {
+	var tables []sqlparser.TableIdent
+	switch expr := node.(type) {
+	case *sqlparser.AliasedTableExpr:
+		tables = append(tables, sqlparser.GetTableName(expr.Expr))
+	case *sqlparser.JoinTableExpr:
+		tables = append(tables, getTables(expr.LeftExpr)...)
+		tables = append(tables, getTables(expr.RightExpr)...)
+	}
+	return tables
+}
+
 func inferColTypeFromExpr(node sqlparser.Expr, colTypeMap map[string]querypb.Type, colNames []string, colTypes []querypb.Type) ([]string, []querypb.Type) {
 	switch node := node.(type) {
 	case *sqlparser.ColName: