我如何使用不同表的记录数创建视图

Question

我需要创建一个视图，其中包含来自 3 个不同 table 但具有相同列的记录数。

也就是这些查询

SELECT COUNT (*) AS count_a from table1 ta
SELECT COUNT (*) AS count_b from table2 tb
SELECT COUNT (*) AS count_c from table3 tc

在视图中引入，join 可以是一个解决方案，但我认为这需要大量工作，同样在每个 table 中都是不同的计数，当使用 join 时它会丢弃一些，如果 table 中有 100、200、15。不，我知道加入是否可以解决这个问题。

我想使用 GROUP_CONCAT 但复习了一下似乎不是一个解决方案，无论如何。简单来说，我想要在一个视图中计算不同 table 的数量，以便显示

想要的结果

count_a	count_b	count_c
100	200	15

提前问候和感谢

PS：现在我不太记得 JOIN 是如何工作的

Answer 1

尝试这样的查询：

SELECT
(SELECT count(*) FROM table1) AS count_a,
(SELECT count(*) FROM table2) AS count_b,
(SELECT count(*) FROM table3) AS count_c;

Answer 2

如果只想显示这3个计数的结果，不进行任何表间连接。我建议使用这样的脚本：

create view desired_result
as select * from (
(SELECT COUNT(*) AS count_a from table1) t1,
(SELECT COUNT(*) AS count_b from table2) t2,
(SELECT COUNT(*) AS count_c from table3) t3);

你可以试试这个fiddle link

Answer 3

如果你喜欢没有JOIN:

SELECT
(SELECT count(*) as count_a FROM table1) AS count_a,
(SELECT count(*) as count_b FROM table2) AS count_b,
(SELECT count(*) as count_c FROM table3) AS count_c;

如果你喜欢 JOIN:

SELECT ta.count_a, tb.count_b, tc.count_c FROM
 (
SELECT COUNT (*) AS count_a, 1 AS rn from table1) ta
JOIN (
SELECT COUNT (*) AS count_b, 1 AS rn from table2) tb
ON ta.rn = tb.rn
 JOIN (
SELECT COUNT (*) AS count_c, 1 AS rn from table3)  tc
ON ta.rn = tc.rn

我如何使用不同表的记录数创建视图

How I create a view with the record count of different tables

mysql

create-view