Bagaimana untuk menggabungkan beberapa pernyataan SELECT ke dalam satu pertanyaan dalam PHP menggunakan MySQL?

Combining Multiple SELECT Statements into a Single Query

In PHP using MySQL, you have multiple SELECT statements in a single script. Each statement retrieves the count of IDs from different tables:

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

You wish to combine these statements into a single query.

Optimizing the Query

To combine the statements, you can use the following syntax:

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

Performance Considerations

Whether or not combining the statements slows down the process depends on the number of tables and the size of the datasets. In general, executing multiple SELECT statements separately will be more efficient than combining them into a single query. However, if you need to access data from multiple tables in a single result set, the performance gain from combining the queries may outweigh the overhead.

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