clickhouse中Nullable与非空字段的建表与类型互转方式

drop table default.tttt
CREATE TABLE default.tttt(
id String,
name String
) ENGINE = MergeTree PARTITION BY id ORDER BY id SETTINGS index_granularity = 8192

insert into `default`.tttt values ('0',null)-- 失败

insert into `default`.tttt values ('1','name1'),('2','name2') --成功

select * from `default`.tttt

alter table `default`.tttt MODIFY COLUMN name Nullable(String) --成功

insert into `default`.tttt values ('3',null) --成功

select * from `default`.tttt

alter table `default`.tttt MODIFY COLUMN name String  --失败，因为记录中存在null值

CREATE TABLE default.tttt2(
id Nullable(String),
name Nullable(String)
) ENGINE = MergeTree PARTITION BY id ORDER BY id SETTINGS index_granularity = 8192

CREATE TABLE default.tttt2(
id String,
name Nullable(String)
) ENGINE = MergeTree PARTITION BY id ORDER BY id SETTINGS index_granularity = 8192
--成功
--直接用空表转换类型
alter table `default`.tttt2 MODIFY COLUMN name String --成功。