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ClickHouse server version 21.6.6
表结构：
dblab-VirtualBox :) desc columns_transformers format TSV;
DESCRIBE TABLE columns_transformers
FORMAT TSV
Query id: fad31334-702a-4360-8976-d9b08eeaec68
i Int64
j Int16
k Int64
3 rows in set. Elapsed: 0.003 sec.
1. ADD COLUMN — 向表中添加一个新列。
格式：
ADD COLUMN [IF NOT EXISTS] name [type] [default_expr] [codec] [AFTER name_after | FIRST]
如果IF NOT EXISTS包含该子句，并且该列已存在，则查询将不会返回错误。如果您指定AFTER name_after（另一列的名称），则该列将添加到表列列表中指定的列之后。如果要在表的开头添加一列，请使用该FIRST子句。否则，该列将添加到表的末尾。对于一系列操作，name_after可以是添加到先前操作之一中的列的名称。
实战：
dblab-VirtualBox :) ALTER TABLE columns_transformers ADD COLUMN Added1 UInt32 FIRST;
ALTER TABLE columns_transformers
ADD COLUMN `Added1` UInt32 FIRST
Query id: 4b24f992-079d-4522-b7be-3eec901c4281
Ok.
0 rows in set. Elapsed: 0.005 sec.
dblab-VirtualBox :) desc columns_transformers format TSV;
DESCRIBE TABLE columns_transformers
FORMAT TSV
Query id: bb93078d-eff2-49fc-9eab-0ec601a6a56e
Added1 UInt32
i Int64
j Int16
k Int64
4 rows in set. Elapsed: 0.004 sec.
dblab-VirtualBox :) ALTER TABLE columns_transformers ADD COLUMN Added2 UInt32 after j;
ALTER TABLE columns_transformers
ADD COLUMN `Added2` UInt32 AFTER j
Query id: 8026002f-6a3f-4028-84d5-5fc4f0152d27
Ok.
0 rows in set. Elapsed: 0.004 sec.
dblab-VirtualBox :) desc columns_transformers format TSV;
DESCRIBE TABLE columns_transformers
FORMAT TSV
Query id: a139da4b-228a-4893-af0e-48935e7eec58
Added1 UInt32
i Int64
j Int16
Added2 UInt32
k Int64
5 rows in set. Elapsed: 0.005 sec.
2. DROP COLUMN — 删除列。
格式：
DROP COLUMN [IF EXISTS] name
实战：
dblab-VirtualBox :) ALTER TABLE columns_transformers DROP COLUMN Added3;
ALTER TABLE columns_transformers
DROP COLUMN Added3
Query id: 3661b1c3-5e81-4073-8f7a-a08b074457cd
Ok.
0 rows in set. Elapsed: 0.008 sec.
dblab-VirtualBox :) desc columns_transformers format TSV;
DESCRIBE TABLE columns_transformers
FORMAT TSV
Query id: 5db10f7a-9da7-4deb-99cd-87e9cb5eaec0
Added1 UInt32
i Int64
j Int16
Added2 UInt32
k Int64
5 rows in set. Elapsed: 0.004 sec.
3. RENAME COLUMN — 重命名现有列。
格式：
RENAME COLUMN [IF EXISTS] name to new_name
实战：
dblab-VirtualBox :) ALTER TABLE columns_transformers RENAME COLUMN k To kk;
ALTER TABLE columns_transformers
RENAME COLUMN k TO kk
Query id: b1d775fb-7919-4c3d-be69-deeae3ddf54c
Ok.
0 rows in set. Elapsed: 0.008 sec.
dblab-VirtualBox :) desc columns_transformers format TSV;
DESCRIBE TABLE columns_transformers
FORMAT TSV
Query id: 474f2c49-05cc-474e-b699-e514559e4b9c
Added1 UInt32
i Int64
j Int16
Added2 UInt32
kk Int64
5 rows in set. Elapsed: 0.003 sec.
4. COMMENT COLUMN — 向列添加文本注释。
格式：
CLEAR COLUMN [IF EXISTS] name IN PARTITION partition_name
实战：
dblab-VirtualBox :) ALTER TABLE columns_transformers COMMENT COLUMN kk 'This is a new coluns';
ALTER TABLE columns_transformers
COMMENT COLUMN kk 'This is a new coluns'
Query id: b1503f1c-f500-4cd5-ab8b-4dce6e234aed
Ok.
0 rows in set. Elapsed: 0.004 sec.
dblab-VirtualBox :) desc columns_transformers format TSV;
DESCRIBE TABLE columns_transformers
FORMAT TSV
Query id: 251d6ed7-e68b-4f19-87cc-95a5b0862b8b
Added1 UInt32
i Int64
j Int16
Added2 UInt32
kk Int64 This is a new coluns
5 rows in set. Elapsed: 0.002 sec.
