Question

我有400多个表，每个表都有一个列时间戳。我想拉出每个表的时间戳的第一行/记录。我不想运行400多个查询，最好的方法是什么？

Answer 1

您可以像这样运行 UNION 查询：

SELECT Id, yourColumn, timestamp FROM Table001 ORDER BY timestamp DESC LIMIT 1
UNION ALL
SELECT Id, yourColumn, timestamp FROM Table002 ORDER BY timestamp DESC LIMIT 1
UNION ALL
SELECT Id, yourColumn, timestamp FROM Table003 ORDER BY timestamp DESC LIMIT 1
ORDER BY timestamp

使用循环创建此语句：

SET @resultQuery = NULL;
SELECT
  GROUP_CONCAT(
    DISTINCT
    CONCAT('SELECT * FROM ', table_name, ' ORDER BY timestamp DESC LIMIT 1 ')
    SEPARATOR '\r\nUNION\r\n'
  )
INTO
  @resultQuery
FROM
  information_schema.COLUMNS
WHERE
  table_schema = '???' AND column_name LIKE '%timestamp';

SELECT @resultQuery;

Answer 2

对400多个表中第一条记录的需求闻起来很糟糕，但如果它们具有相同的模式，则可以使用$('#calendar').fullCalendar( 'rerenderEvents' );：

UNION ALL

MySQL从多个表中选择一条记录

2 个答案: