mysql - how to count the two count function's return value in once sql query -

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i have 3 tables a,b,c.their relation a.id b's foreign key , b.id c's foreign key.i need sum value when b.id = c.id , a.id = b.id ,i can count number query twice. need way count summation once time !

my inefficient solution

select count(c.id) c,b c.id = b.id;  //return value x select count(a.id) c,b a.id = b.id;  //return value y select x + y; // count summation fo x , y

how can optimize ? thks! :)

ps：

my question galaxql,which sql interactive tutorial.i have abstract problem,more detail can check section 17.select...group by... having...

you can these things in 1 query. instance, this:

select (select count(*) c join b on c.id = b.id) +        (select count(*) c join on c.id = a.id)

(your second query not parse because a not recognized table alias.)

in case, if learning sql, first thing should learn modern join syntax. implicit joins using out of date 15 years ago , have been part of ansi standard on 20 years. learn proper join syntax.


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