Question

Can some one tell me the difference between INSTR and LIKE in Oracle?

Which one is faster in Oracle10g?

Answer 1

That depends on the data and on the pattern. If you use like 'a%', then Oracle can use a BTree indexes to look up the matches because it can search the btree with the start of the pattern and then consider only the subtree.

This doesn’t work for LIKE '%a' but you can work around this by creating a calculated column which reverses all values from the column you want to search (so you get the pattern above).

If you use hashed indexes, there is little that Oracle can do but scan the whole index. It might sill be faster when there are only few different values.

I’m not sure whether INSTR can ever use an index because it has no fixed anchor.

So like with all performance questions:

1. Fill the database with some realistic test data and run some tests.
2. Always write your code in a way that it can be optimized easily later, when you know about the bottlenecks
3. Never guess what might be slow. You’ll be wrong 90% of the time. Always measure.