单个查询中的多个select语句

Question

我在php(mysql)中生成一个报告,

例如:

`select count(id) as tot_user from user_table
 select count(id) as tot_cat from cat_table
 select count(id) as tot_course from course_table`

像这样我有12张桌子.

我可以在单个查询中进行.如果我做了？流程变慢了？

Answer 1

SELECT  (
    SELECT COUNT(*)
    FROM   user_table
    ) AS tot_user,
    (
    SELECT COUNT(*)
    FROM   cat_table
    ) AS tot_cat,
    (
    SELECT COUNT(*)
    FROM   course_table
    ) AS tot_course

Answer 2

如果您使用MyISAM表,最快的方法是直接查询统计信息:

select table_name, table_rows 
     from information_schema.tables 
where 
     table_schema='databasename' and 
     table_name in ('user_table','cat_table','course_table')

如果您有InnoDB,则必须使用count()进行查询,因为information_schema.tables中的报告值是错误的.

Answer 3

你当然可以将Ben Agregation声明作为Ben James的假设,但是这将产生一个包含尽可能多的列的视图.另一种方法可能如下:

SELECT COUNT(user_table.id) AS TableCount,'user_table' AS TableSource FROM user_table
UNION SELECT COUNT(cat_table.id) AS TableCount,'cat_table' AS TableSource FROM cat_table
UNION SELECT COUNT(course_table.id) AS TableCount, 'course_table' AS TableSource From course_table;

关于这样的approch的好处是,您可以显式编写Union语句并生成视图或创建临时表,以保存使用变量代替表名从Proc cals连续添加的值.我倾向于更多地使用后者,但这实际上取决于个人偏好和应用.如果您确定表永远不会更改,那么您希望数据采用单行格式,并且您不会添加表.坚持Ben James的解决方案.否则我建议灵活性,你总是可以破解交叉表结构.

Answer 4

select RTRIM(A.FIELD) from SCHEMA.TABLE A where RTRIM(A.FIELD) =  ('10544175A') 
 UNION  
select RTRIM(A.FIELD) from SCHEMA.TABLE A where RTRIM(A.FIELD) = ('10328189B') 
 UNION  
select RTRIM(A.FIELD) from SCHEMA.TABLE A where RTRIM(A.FIELD) = ('103498732H')

Answer 5

SELECT t1.credit, 
       t2.debit 
FROM   (SELECT Sum(c.total_amount) AS credit 
        FROM   credit c 
        WHERE  c.status = "a") AS t1, 
       (SELECT Sum(d.total_amount) AS debit 
        FROM   debit d 
        WHERE  d.status = "a") AS t2