ALTER TABLE [Employee]
ALTER COLUMN [Salary] NUMERIC(22,5) NOT NULL

对于Oracle数据库:

VARCHAR2(255 CHAR);

运行ALTER COLUMN而不提及属性NOT NULL将导致该列被更改为可空，如果它已经不是。因此，您需要首先检查列是否为空，如果不是，则指定属性not NULL。或者，您可以使用下面的语句预先检查列的可空性，并运行具有正确属性的命令。

IF COLUMNPROPERTY(OBJECT_ID('Employee', 'U'), 'Salary', 'AllowsNull')=0
    ALTER TABLE [Employee]
        ALTER COLUMN [Salary] NUMERIC(22,5) NOT NULL
ELSE        
    ALTER TABLE [Employee]
        ALTER COLUMN [Salary] NUMERIC(22,5) NULL

ALTER TABLE [table_name] ALTER COLUMN [column_name] varchar(150)

有趣的方法可以在这里找到:如何扩大你的专栏没有停机由spaghettidba

If you try to enlarge this column with a straight “ALTER TABLE” command, you will have to wait for SQLServer to go through all the rows and write the new data type ALTER TABLE tab_name ALTER COLUMN col_name new_larger_data_type; To overcome this inconvenience, there is a magic column enlargement pill that your table can take, and it’s called Row Compression. (...) With Row Compression, your fixed size columns can use only the space needed by the smallest data type where the actual data fits.

当表在ROW级别被压缩时，ALTER table ALTER COLUMN是仅元数据的操作。

ALTER TABLE "Employee" MODIFY ("Salary" NUMERIC(2,5));