MySQL Database common

Removing duplicate records Distinct example: SELECT DISTINCT

Union union query, merge the query results of 2 SELECT statements to use the knife all to ensure that the data is displayed (can display 2 times the same record)
Usage (SELECT statement) union ALL (SELECT)

Sort
Sort the result of a word statement
1. Wrap the word statement in parentheses
2. ORDER BY of Word statement
Only the order by mate limit is valid because the Union is optimized for order by without a limit sentence (ignored) when it makes a word statement


Any and in do use the same example xxx in XXX xxx=any (XXX)
Some (collection) the same usage as any in the collection
Not any is not one of the

Summary; =any in
!=all not in
Some and any intent words

MySQL Database common