SQL COUNT多表联合统计技巧

在 SQL 中，我们可以使用 COUNT 函数对多张表进行联合统计。具体的方法取决于我们需要的统计结果是什么，以下是一些多表联合统计的技巧：

1. 统计两个表的行数：

SELECT
    (SELECT COUNT(*) FROM table1) AS count_table1,
    (SELECT COUNT(*) FROM table2) AS count_table2;

2. 统计两个表中满足条件的行数：

SELECT
    (SELECT COUNT(*) FROM table1 WHERE condition1) AS count_table1_condition,
    (SELECT COUNT(*) FROM table2 WHERE condition2) AS count_table2_condition;

3. 统计两个表中的总行数：

SELECT
    (SELECT COUNT(*) FROM table1) + (SELECT COUNT(*) FROM table2) AS total_count;

4. 统计两个表中重复的行数：

SELECT COUNT(*) AS duplicate_count
FROM (
    SELECT column1, column2
    FROM table1
    UNION ALL
    SELECT column1, column2
    FROM table2
) AS combined_tables
GROUP BY column1, column2
HAVING COUNT(*) > 1;

以上是一些常见的多表联合统计技巧，根据具体需求可以进行进一步的调整和拓展。