带有数据和标题的 MySQL CSV 导出

Question

我也尝试从带有标头的 MySQL 数据库中导出 CSV。但我收到以下错误-

ERROR 1222 (21000): The used SELECT statements have a different number of columns

MySQL 查询如下-

SELECT * FROM (
  (SELECT COLUMN_NAME
    FROM INFORMATION_SCHEMA.COLUMNS
    WHERE TABLE_NAME = 'ORDERS'
    AND TABLE_SCHEMA = 'REMOTE'
    ORDER BY ORDINAL_POSITION)
  UNION ALL
  (SELECT * FROM ORDERS WHERE orderDate>='2018-05-07')) AS TBL
INTO OUTFILE 'C:/xampp/htdocs/WES/DBScript/SS_Orders.csv'
FIELDS TERMINATED BY ','
ENCLOSED BY '"'
LINES TERMINATED BY '\n';

Answer 1

通常你必须这样做：

SELECT *
FROM (
    select 'A', 'B', 'C'
    union all
    select a, b, c from table
    ) t
INTO OUTFILE [...]

请注意，您必须确保所有列数据类型都正确匹配，这意味着它们都需要是 varchar 或类似的。

对于标题，您可以通过以下方式自动化它们：

SELECT * FROM (
SELECT MAX(CASE WHEN ORDINAL_POSITION = 1 THEN COLUMN_NAME END),
    MAX(CASE WHEN ORDINAL_POSITION = 2 THEN COLUMN_NAME END),
    MAX(CASE WHEN ORDINAL_POSITION = 3 THEN COLUMN_NAME END),
    MAX(CASE WHEN ORDINAL_POSITION = 4 THEN COLUMN_NAME END),
    MAX(CASE WHEN ORDINAL_POSITION = 5 THEN COLUMN_NAME END),
    MAX(CASE WHEN ORDINAL_POSITION = 6 THEN COLUMN_NAME END),
    [...]
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'ORDERS'
    AND TABLE_SCHEMA = 'REMOTE'
UNION ALL
SELECT [...]
) t
INTO OUTFILE [...]

但您仍然需要知道列数。如果您想动态地执行此操作，则本质上将需要动态 SQL。

It may be easier to just write a Python script to do it.