MySQL查询中答案为true，false

Question

I was not too long ago studying java, so maybe I have a stupid question.

I have a table, where i store some info. And i want to check in this table on availability of some information (it will be only one line), and if yes - take from this line, the information in a particular column, if no - do another thing.

I really don`t know how to do this. My idea was something like this: at first - check the table:

SELECT * FROM tablename WHERE nickname = "kvant";

then if true, do another query with searching info. and do this with condition if\\else. but all my attempts not turn.

I hope for your help, sorry for my awry English.

Answer 1

Check if the data exists like this:

IF EXISTS(SELECT * FROM tablename WHERE nickname = "kvant")
BEGIN
    --value is found so go ahead 
END
ELSE
    --value not found
BEGIN
END

Answer 2

One simple way is to query the database and get the result. If result!=Null {//do something} else {//Do something}

(Can use try - catch as well)

Answer 3

Pure java possible solution:

Try to get that value in the query. Get the ResultSet rs of that query and:

if(rs.next()) {
    String value = rs.getString("value"); //Assuming the column is value and that it is a String.
    //Do whatever you want with the value
} else {
    //The other thing
}

If you can not take the value from the first ResultSet, do another query in the if.

Answer 4

write in sql like select case exists (select * from yourtable where condition) then 'dothis thing' else 'dootherthing' from 'yourtable' where 'yourcondition'

since you wanted to run some other query after you know you have some conditon exists.