改变表中添加列
ALTER TABLE table_name
ADD column_name datatype;
sql改变表中添加列如果存在的话
IF NOT EXISTS (
SELECT
*
FROM
INFORMATION_SCHEMA.COLUMNS
WHERE
TABLE_NAME = 'table_name' AND COLUMN_NAME = 'col_name')
BEGIN
ALTER TABLE table_name
ADD col_name data_type NULL
END;