Question

说我有以下内容：

CREATE TABLE newtable AS (
SELECT @rownum:=@rownum+1 as rownum, name, age FROM (
    SELECT name, age FROM clubAmembers
    UNION
    SELECT name, age FROM clubBmembers
)
) AS atable

我怎样才能使它能够在SELECT联合之前“坚持在表格开头的新行”，以便从以下开始：

rownum | name| age
1 | "Jordan" | 6  <-- This is an arbitrarily inserted record with name="Jordan" age="6" that is not a part of any of the clubAmembers or clubBmembers table.

表格的其余部分（rownum 2及以后）将包含与clubAmembers联盟的实际结果，然后是clubBmembers。

基本上我正在寻找：创建表插入一行“Jordan”| 6 使用union执行select，使得第一行之后的行以“rownum = 2”开头，来自clubAmembers的所有数据等等。

如何做到最好？

Answer 1

我不确定我是否做对了。但是你为什么不添加这样的另一个联盟：

CREATE TABLE newtable AS (
SELECT @rownum:=@rownum+1 as rownum, name, age FROM (
    SELECT 1, "Jordan", 6
    UNION ALL
    SELECT name, age FROM clubAmembers
    UNION ALL
    SELECT name, age FROM clubBmembers
)
) AS atable

Answer 2

“在表的开头”对关系数据库没有真正的意义，因为在使用ORDER BY子句之前不能保证返回的订单结果，此时磁盘上的顺序无论如何都成为一个有争议的点

在您的情况下，由于您要保证结果子句中的订单（因此订购@rownum），您必须使用ORDER BY。例如：

CREATE TABLE newtable AS (
    SELECT @rownum:=@rownum+1 as rownum, name, age 
    FROM (
        SELECT 'Jordan' AS name, 6 AS age, 0 AS ord
        UNION
        SELECT name, age, 1 AS ord FROM clubAmembers
        UNION
        SELECT name, age, 1 AS ord FROM clubBmembers
        ORDER BY ord
    )
) AS atable

请注意，这绝不保证clubAmembers中的行比rownum中的行低clubBmembers。如果您想保证clubAmembers的{{1}}较低rownum，同时保留UNION（与UNION ALL）的语义，则可以使用以下内容：

CREATE TABLE newtable AS (
    SELECT @rownum:=@rownum+1 as rownum, name, age 
    FROM (
        SELECT 'Jordan' AS name, 6 AS age, 0 AS ord
        UNION ALL
        SELECT name, age, 1 AS ord FROM clubAmembers
        UNION ALL
        SELECT name, age, 2 AS ord FROM clubBmembers AS b
        WHERE NOT EXISTS(SELECT 1 FROM clubAmembers AS a 
                         WHERE a.name = b.name AND a.age = b.age)
        ORDER BY ord
    )
) AS atable

请注意，{name，age}可以在clubXmembers表格中重复，您需要添加DISTINCT：

...
SELECT DISTINCT name, age, 1 AS ord FROM clubAmembers
UNION ALL
...

根据评论中的请求，如果你有clubCmembers表，你会这样做：

CREATE TABLE newtable AS (
    SELECT @rownum:=@rownum+1 as rownum, name, age 
    FROM (
        SELECT 'Jordan' AS name, 6 AS age, 0 AS ord
        UNION ALL
        SELECT name, age, 1 AS ord FROM clubAmembers
        UNION ALL
        SELECT name, age, 2 AS ord FROM clubBmembers AS b
        WHERE NOT EXISTS(SELECT 1 FROM clubAmembers AS a 
                         WHERE a.name = b.name AND a.age = b.age)
        SELECT name, age, 3 AS ord FROM clubCmembers AS c
        WHERE NOT EXISTS(SELECT 1 FROM clubAmembers AS a 
                         WHERE a.name = c.name AND a.age = c.age)
        AND NOT EXISTS(SELECT 1 FROM clubBmembers AS b
                       WHERE b.name = c.name AND b.age = c.age)
        ORDER BY ord
    )
) AS atable

Answer 3

您可以将create table statmenet与insert statmenet分开：

创建表格（你必须知道哪些列是gona）
插入您的第一条记录(INSERT INTO .... Values(...)）
使用您的语句，但使用insert into代替create table，如：INSERT INTO YourNewTable.... Values(YourSubQuery)（Nr和tye列必须与您的子查询匹配）

Answer 4

我应该这样做，我相信：

CREATE TABLE newtable AS (
  SELECT (@rownum:=IFNULL(@rownum,0)+1)+1 as rownum, name, age FROM (
    SELECT name, age FROM clubAmembers
    UNION
    SELECT name, age FROM clubBmembers
  ) AS s
  UNION ALL
  SELECT 1, 'Jordan', 6
) AS atable

SQL小提琴演示：http://sqlfiddle.com/#!2/ab825/6

如何在联合之前在mysql中插入一行？

4 个答案: