postgreSQL將列數據類型更改爲不帶時區的時間戳

Question

我想將文本中的一列數據更改爲時間戳類型。我的數據中沒有時區。我的數據格式是28-03-17 17:22，包括時間和日期，但沒有時區。換句話說，我所有的數據都在同一時區。我該怎麼做？

我嘗試了以下多種方法，但我仍然找不到正確的方法。希望您能夠幫助我。

當然，如果我的麻煩可以解決，我可以建立一個新表格。

alter table AB 
alter create_time type TIMESTAMP; 

ERROR: column "create_time" cannot be cast automatically to type timestamp without time zone 
HINT: You might need to specify "USING create_time::timestamp without time zone". 
********** Error ********** 

ERROR: column "create_time" cannot be cast automatically to type timestamp without time zone 
SQL state: 42804 
Hint: You might need to specify "USING create_time::timestamp without time zone". 

alter table AB 
alter create_time type TIMESTAMP without time zone; 

ERROR: column "create_time" cannot be cast automatically to type timestamp without time zone 
HINT: You might need to specify "USING create_time::timestamp without time zone". 
********** Error ********** 

ERROR: column "create_time" cannot be cast automatically to type timestamp without time zone 
SQL state: 42804 
Hint: You might need to specify "USING create_time::timestamp without time zone". 

alter table AB 
alter create_time::without time zone type TIMESTAMP; 

ERROR: syntax error at or near "::" 
LINE 2: alter create_time::without time zone type TIMESTAM 
         ^
********** Error ********** 

ERROR: syntax error at or near "::" 
SQL state: 42601 
Character: 50 

alter table AB 
alter create_time UTC type TIMESTAMP; 

ERROR: syntax error at or near "UTC" 
LINE 2: alter create_time UTC type TIMESTAMP; 
         ^
********** Error ********** 

ERROR: syntax error at or near "UTC" 
SQL state: 42601 
Character: 50 

Answer 1

如果create_time是有效的日期值類型的文字，這將是更容易的改變進行如下操作（宜首先做一個錶轉儲爲備份）：

-- Create a temporary TIMESTAMP column 
ALTER TABLE AB ADD COLUMN create_time_holder TIMESTAMP without time zone NULL; 

-- Copy casted value over to the temporary column 
UPDATE AB SET create_time_holder = create_time::TIMESTAMP; 

-- Modify original column using the temporary column 
ALTER TABLE AB ALTER COLUMN create_time TYPE TIMESTAMP without time zone USING create_time_holder; 

-- Drop the temporary column (after examining altered column values) 
ALTER TABLE AB DROP COLUMN create_time_holder; 

Answer 2

USING...而來的類型後：

... alter create_time type TIMESTAMP USING create_time::TIMESTAMP; 

Answer 3

沒有指定原始類型CREATE_TIME的，所以我認爲它是時區與時區（因爲類型DATE或帶有時區的TIMESTAMP在嘗試更改爲不帶時區的TIMESTAMP時不應出現上述錯誤）。由於時間戳記除了時間日期信息，你需要補充你的ALTER語句的最新信息，如：

ALTER TABLE AB ALTER COLUMN create_time TYPE TIMESTAMP without time zone USING date('20170327') + create_time; 

如果你有相應的DATE列（比如，CREATE_DATE），你可以通過它到date（）函數，如：

ALTER TABLE AB ALTER COLUMN create_time TYPE TIMESTAMP without time zone USING date(create_date) + create_time; 

Answer 4

從BIGINT改變列的數據類型到時間戳（對於曆元到時間戳）

alter table <tablename> alter column <columnname> type timestamp without time zone using to_timestamp(<columnname>) AT TIME ZONE 'UTC'; 

爲例如;

alter table AB alter column col type timestamp without time zone using to_timestamp(col) AT TIME ZONE 'UTC'; 

從時間戳改變列的數據類型爲bigint（對於時間戳曆元）

alter table <tablename> alter column <columnname> type bigint using extract(EPOCH from <columnname>); 

爲例如;

alter table AB alter column col type bigint using extract(EPOCH from col);