multi_index query [WHERE]

Question

How do we query tables in EOS? Specifically like the WHERE clause in SQL Database?

I see examples that uses iterator to find if the record exists, however I don't see it as the right approach specially if we have large sets of data.

I can use get and find for the primary key, but what about for other keys?

Answer 1

You can use primary key or index to query the data.

For the query where, the index provide find and lower_bound and upper_bound method, which returns the iterator, if you have more than one rows, just use code like it below:

while(iter != xxx.end()) {
   iter++;
}

for lower_bound or upper_bound, or

while(iter != xxx.end() && iter->yourdata == yourquery) {
   iter++;
}

for find.