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chore: refine the default column value error #11169

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Apr 21, 2023
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chore: refine the default column value error #11169

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220 changes: 109 additions & 111 deletions docs/doc/14-sql-commands/00-ddl/20-table/10-ddl-create-table.md
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Original file line number Diff line number Diff line change
Expand Up @@ -23,8 +23,8 @@ Databend aims to be easy to use by design and does NOT require any of those oper
```sql
CREATE [TRANSIENT] TABLE [IF NOT EXISTS] [db.]table_name
(
<column_name> <data_type> [ NOT NULL | NULL] [ { DEFAULT <expr> }],
<column_name> <data_type> [ NOT NULL | NULL] [ { DEFAULT <expr> }],
<column_name> <data_type> [ NOT NULL | NULL] [ { DEFAULT <constant_expr> }],
<column_name> <data_type> [ NOT NULL | NULL] [ { DEFAULT <constant_expr> }],
...
) [CLUSTER BY(<expr> [, <expr>, ...] )]

Expand Down Expand Up @@ -217,9 +217,9 @@ DESC t_null;

## Default Values
```sql
DEFAULT <expression>
DEFAULT <constant_expression>
```
Specifies a default value inserted in the column if a value is not specified via an INSERT or CREATE TABLE AS SELECT statement.
Specify a default value(constant expression) inserted in the column if a value is not specified via an INSERT or CREATE TABLE AS SELECT statement.

For example:
```sql
Expand Down Expand Up @@ -260,153 +260,143 @@ Databend’s syntax is difference from MySQL mainly in the data type and some sp

### Create Table

Create a table with a default value for a column (in this case, the `genre` column has 'General' as the default value):

```sql
CREATE TABLE test(a BIGINT UNSIGNED, b VARCHAR , c VARCHAR DEFAULT concat(b, '-b'));
CREATE TABLE books (
id BIGINT UNSIGNED,
title VARCHAR,
genre VARCHAR DEFAULT 'General'
);
```

Describe the table to confirm the structure and the default value for the `genre` column:

```sql
DESC test;
+-------+--------+------+---------------+
| Field | Type | Null | Default |
+-------+--------+------+---------------+
| a | UInt64 | NO | 0 |
| b | String | NO | |
| c | String | NO | concat(b, -b) |
+-------+--------+------+---------------+
DESC books;
+-------+-----------------+------+---------+-------+
| Field | Type | Null | Default | Extra |
+-------+-----------------+------+---------+-------+
| id | BIGINT UNSIGNED | NO | 0 | |
| title | VARCHAR | NO | "" | |
| genre | VARCHAR | NO | 'General'| |
+-------+-----------------+------+---------+-------+
```

Insert a row without specifying the `genre`:

```sql
INSERT INTO test(a,b) VALUES(888, 'stars');
INSERT INTO books(id, title) VALUES(1, 'Invisible Stars');
```

Query the table and notice that the default value 'General' has been set for the `genre` column:

```sql
SELECT * FROM test;
+------+-------+---------+
| a | b | c |
+------+-------+---------+
| 888 | stars | stars-b |
+------+-------+---------+
SELECT * FROM books;
+----+----------------+---------+
| id | title | genre |
+----+----------------+---------+
| 1 | Invisible Stars| General |
+----+----------------+---------+
```

### Create Table ... Like

The following example indicates that the command does not copy any data from an existing table but only the column definitions:
Create a new table (`books_copy`) with the same structure as an existing table (`books`):

```sql
CREATE TABLE test2 LIKE test;

DESC test2;
+-------+--------+------+---------------+
| Field | Type | Null | Default |
+-------+--------+------+---------------+
| a | UInt64 | NO | 0 |
| b | String | NO | |
| c | String | NO | concat(b, -b) |
+-------+--------+------+---------------+

INSERT INTO test2(a,b) VALUES(888, 'stars');

-- The new table contains inserted data only. Data in the existing table was not copied.
SELECT * FROM test2;
+------+-------+---------+
| a | b | c |
+------+-------+---------+
| 888 | stars | stars-b |
+------+-------+---------+
CREATE TABLE books_copy LIKE books;
```

The following example indicates that the command does not copy attributes of an existing table:
Check the structure of the new table:

```sql
CREATE TRANSIENT TABLE tb_01(id int, c1 varchar) CLUSTER BY(id);

SET hide_options_in_show_create_table=0

SHOW CREATE TABLE tb_01;

Table|Create Table |
-----+---------------------------------------------------------------------------------------------------------------------------------------+
tb_01|CREATE TABLE `tb_01` (¶ `id` INT,¶ `c1` VARCHAR¶) ENGINE=FUSE CLUSTER BY (id) TRANSIENT='T' COMPRESSION='lz4' STORAGE_FORMAT='native'|


CREATE TABLE tb_02 LIKE tb_01;

-- The attributes CLUSTER BY and TRANSIENT were not copied to the new table.

SHOW CREATE TABLE tb_02;

Table|Create Table |
-----+---------------------------------------------------------------------------------------------------------+
tb_02|CREATE TABLE `tb_02` (¶ `id` INT,¶ `c1` VARCHAR¶) ENGINE=FUSE COMPRESSION='lz4' STORAGE_FORMAT='native'|

-- Add CLUSTER BY using ALTER TABLE.

ALTER TABLE tb_02 CLUSTER BY(id);

Table|Create Table |
-----+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
tb_02|CREATE TABLE `tb_02` (¶ `id` INT,¶ `c1` VARCHAR¶) ENGINE=FUSE CLUSTER BY (id) COMPRESSION='lz4' SNAPSHOT_LOCATION='1/21465/_ss/6b4b16900a4c4134b7dab535b1c93546_v2.json' STORAGE_FORMAT='native'|

-- Not all the table attributes can be added using ALTER TABLE.

ALTER TABLE tb_02 TRANSIENT='T';
DESC books_copy;
+-------+-----------------+------+---------+-------+
| Field | Type | Null | Default | Extra |
+-------+-----------------+------+---------+-------+
| id | BIGINT UNSIGNED | NO | 0 | |
| title | VARCHAR | NO | "" | |
| genre | VARCHAR | NO | 'General'| |
+-------+-----------------+------+---------+-------+
```

SQL Error [1105] [HY000]: Code: 1005, displayText = error:
--> SQL:1:83
|
1 | /* ApplicationName=DBeaver 23.0.1 - SQLEditor <Script-1.sql> */ alter table tb_02 TRANSIENT='T'
| ----- ^^^^^^^^^ expected `RENAME`, `ADD`, `DROP`, `CLUSTER`, `RECLUSTER`, `FLASHBACK`, or 1 more ...
| |
| while parsing `ALTER TABLE [<database>.]<table> <action>`
Insert a row into the new table and notice that the default value for the `genre` column has been copied:

.
```sql
INSERT INTO books_copy(id, title) VALUES(1, 'Invisible Stars');

SELECT * FROM books_copy;
+----+----------------+---------+
| id | title | genre |
+----+----------------+---------+
| 1 | Invisible Stars| General |
+----+----------------+---------+
```

### Create Table ... As

Create a new table (`books_backup`) that includes data from an existing table (`books`):

```sql
CREATE TABLE test3 AS SELECT * FROM test2;
CREATE TABLE books_backup AS SELECT * FROM books;
```

Describe the new table and notice that the default value for the `genre` column has NOT been copied:

```sql
DESC test3;
+-------+--------+------+---------------+
| Field | Type | Null | Default |
+-------+--------+------+---------------+
| a | UInt64 | NO | 0 |
| b | String | NO | |
| c | String | NO | concat(b, -b) |
+-------+--------+------+---------------+
DESC books_backup;
+-------+-----------------+------+---------+-------+
| Field | Type | Null | Default | Extra |
+-------+-----------------+------+---------+-------+
| id | BIGINT UNSIGNED | NO | 0 | |
| title | VARCHAR | NO | "" | |
| genre | VARCHAR | NO | NULL | |
+-------+-----------------+------+---------+-------+
```

Query the new table and notice that the data from the original table has been copied:

```sql
SELECT * FROM test3;
+------+-------+---------+
| a | b | c |
+------+-------+---------+
| 888 | stars | stars-b |
+------+-------+---------+
SELECT * FROM books_backup;
+----+----------------+---------+
| id | title | genre |
+----+----------------+---------+
| 1 | Invisible Stars| General |
+----+----------------+---------+
```

### Create Transient Table

Create a transient table (temporary table) that automatically deletes data after a specified period of time:

```sql
-- Create a transient table
CREATE TRANSIENT TABLE mytemp (c bigint);
CREATE TRANSIENT TABLE visits (
visitor_id BIGINT
);

-- Insert values
insert into mytemp values(1);
insert into mytemp values(2);
insert into mytemp values(3);

-- Only one snapshot is stored. This explains why the Time Travel feature does not work for transient tables.
select count(*) from fuse_snapshot('default', 'mytemp');
+---------+
| count() |
+---------+
| 1 |
INSERT INTO visits VALUES(1);
INSERT INTO visits VALUES(2);
INSERT INTO visits VALUES(3);

-- Check the inserted data
SELECT * FROM visits;
+-----------+
| visitor_id |
+-----------+
| 1 |
| 2 |
| 3 |
+-----------+
```

### Create Table ... Snapshot_Location

Create a table from a specific snapshot, allowing you to create a new table based on the data at a specific point in time:

```sql
```sql
CREATE TABLE members
(
Expand Down Expand Up @@ -456,9 +446,17 @@ Amy

### Create Table ... External_Location

Create a table with data stored on an external location, such as Amazon S3:

```sql
-- Create a table named `mytable` and specify the location `s3://testbucket/admin/data/` for the data storage
CREATE TABLE mytable(a int)
's3://testbucket/admin/data/'
connection=(ACCESS_KEY_ID='<your_aws_key_id>' SECRET_ACCESS_KEY='<your_aws_secret_key>' endpoint_url='https://s3.amazonaws.com');
CREATE TABLE mytable (
a INT
)
external_location='s3://testbucket/admin/data/'
connection=(
ACCESS_KEY_ID='<your_aws_key_id>'
SECRET_ACCESS_KEY='<your_aws_secret_key>'
endpoint_url='https://s3.amazonaws.com'
);
```
86 changes: 59 additions & 27 deletions docs/doc/14-sql-commands/00-ddl/20-table/90-alter-table-column.md
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Expand Up @@ -16,37 +16,69 @@ ALTER TABLE can also handle table clustering. For more information, refer to the
## Syntax

```sql
ALTER TABLE [IF EXISTS] <name> ADD COLUMN <column_name> <data_type> [ NOT NULL | NULL] [ { DEFAULT <expr> }]
ALTER TABLE [IF EXISTS] <name> ADD COLUMN <column_name> <data_type> [ NOT NULL | NULL] [ { DEFAULT <constant_expr> }]
ALTER TABLE [IF EXISTS] <name> DROP COLUMN <column_name>
```

## Examples

### Add Column

Add a new column to an existing table:

```sql
DESC books;

Field |Type |Null|Default |Extra|
--------+---------+----+------------+-----+
price |FLOAT |NO |0.00 | |
pub_time|TIMESTAMP|NO |'1900-01-01'| |
author |VARCHAR |NO |"" | |

ALTER TABLE books ADD COLUMN region varchar;
DESC books;

Field |Type |Null|Default |Extra|
--------+---------+----+------------+-----+
price |FLOAT |NO |0.00 | |
pub_time|TIMESTAMP|NO |'1900-01-01'| |
author |VARCHAR |NO |"" | |
region |VARCHAR |NO |"" | |

ALTER TABLE books DROP COLUMN region;
DESC books;

Field |Type |Null|Default |Extra|
--------+---------+----+------------+-----+
price |FLOAT |NO |0.00 | |
pub_time|TIMESTAMP|NO |'1900-01-01'| |
author |VARCHAR |NO |"" | |
-- Create a table
CREATE TABLE students (
id BIGINT,
name VARCHAR
);

-- Add a new column 'age' to the 'students' table
ALTER TABLE students ADD COLUMN age INT;
```

### Drop Column

Remove an existing column from a table:

```sql
-- Create a table with three columns
CREATE TABLE employees (
id BIGINT,
name VARCHAR,
department VARCHAR
);

-- Remove the 'department' column from the 'employees' table
ALTER TABLE employees DROP COLUMN department;
```

### Add Column with Default Value

Add a new column to an existing table with a default value:

```sql
-- Create a table
CREATE TABLE orders (
id BIGINT,
item VARCHAR
);

-- Add a new column 'status' with a default value 'Pending' to the 'orders' table
ALTER TABLE orders ADD COLUMN status VARCHAR DEFAULT 'Pending';
```

### Add Column with NOT NULL Constraint

Add a new column to an existing table with a NOT NULL constraint, which ensures that a value must be assigned to the column:

```sql
-- Create a table
CREATE TABLE products (
id BIGINT,
name VARCHAR
);

-- Add a new column 'price' with a NOT NULL constraint to the 'products' table
ALTER TABLE products ADD COLUMN price INT NOT NULL;
```
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