$CLICKHOUSE_CLIENT-q"DROP TABLE IF EXISTS alter_table"
$CLICKHOUSE_CLIENT-q"CREATE TABLE alter_table (a UInt8, b Int16, c Float32, d String, e Array(UInt8), f Nullable(UUID), g Tuple(UInt8, UInt16)) ENGINE = MergeTree ORDER BY a"
function thread1()
{
while true;do$CLICKHOUSE_CLIENT--query"SELECT name FROM system.columns UNION ALL SELECT name FROM system.columns FORMAT Null";done
}
function thread2()
{
while true;do$CLICKHOUSE_CLIENT-n--query"ALTER TABLE alter_table ADD COLUMN h String; ALTER TABLE alter_table MODIFY COLUMN h UInt64; ALTER TABLE alter_table DROP COLUMN h;";done