Index indexa fields in table A, A, query using
Select columns from A where A like '% zhang SAN for index failure occurs?
Like grammar like '% zhang SAN' index fails, like 'Joe Smith %' index is normal?
Excuse me why
CodePudding user response:
In MySQL, for example, field index on is actually a b-tree indexes; B-tree indexes can be used like a query, but like the back to a constant string, cannot begin with %Therefore, select columns from A where A like '% zhang SAN for index failure occurs,
You can see the official document:
https://dev.mysql.com/doc/refman/8.0/en/index-btree-hash.html
CodePudding user response:
Index is sorting, or line up more intuitive,Like zhang SAN %, actually you are looking for is' zhang SAN XXX ', as long as all the parts' zhang 'at the beginning of the return can, this part is a continuous, don't need a full table scan,
Zhang SAN like '%', actually you are looking for is' XXX zhang SAN, this part is discontinuous in the index, if need to return to the results, only a full table scan,
CodePudding user response:
The most left the principle of the index