Initial work to support MemSQL/SingleStore

Issue: pingcap#309

- `WITH CONSISTENT SNAPSHOT` is not supported by MemSQL.
- `SHOW CREATE DATABASE` is not supported by MemSQL.

v4/export/sql.go

@@ -50,7 +50,8 @@ func ShowCreateDatabase(db *sql.Conn, database string) (string, error) {
 	query := fmt.Sprintf("SHOW CREATE DATABASE `%s`", escapeString(database))
 	err := simpleQuery(db, query, handleOneRow)
 	if err != nil {
-		return "", errors.Annotatef(err, "sql: %s", query)
+		// return "", errors.Annotatef(err, "sql: %s", query)
+		return "CREATE DATABASE `%s`", nil
 	}
 	return oneRow[1], nil
 }
@@ -625,7 +626,11 @@ func createConnWithConsistency(ctx context.Context, db *sql.DB) (*sql.Conn, erro
 	query = "START TRANSACTION /*!40108 WITH CONSISTENT SNAPSHOT */"
 	_, err = conn.ExecContext(ctx, query)
 	if err != nil {
-		return nil, errors.Annotatef(err, "sql: %s", query)
+		query = "START TRANSACTION"
+		_, err = conn.ExecContext(ctx, query)
+		if err != nil {
+			return nil, errors.Annotatef(err, "sql: %s", query)
+		}
 	}
 	return conn, nil
 }