What does SQL replace or

（1） use UNION Replace OR ( For index columns )
Usually , use UNION Replace WHERE In Clause OR Will play a better effect . Use for non indexed columns OR Will cause a full table scan . pay attention to , The above rules are only valid for multiple index columns . If there is column
Not indexed , Query efficiency may be because you don't have a choice OR And lower . In the following example , LOC_ID and REGION There's an index on it .
Efficient :
SELECT LOC_ID , LOC_DESC, REGION FROM LOCATION WHERE LOC_ID = 10 UNION SELECT LOC_ID , LOC_DESC ,REGION FROM LOCATION WHERE REGION = “MELBOURNE”
Inefficient :
SELECT LOC_ID , LOC_DESC, REGION FROM LOCATION WHERE LOC_ID = 10 OR REGION = “MELBOURNE”
If you insist on using OR, Then you need to return the index column with the least number of records, which is written at the top .

（2） use IN To replace OR