Chapter 3. Data retrieval (query)---Select, top, DISTINCT

======select data Query ======

To query all the data in a table:

SELECT * FROM table name

Select Column Name 1, column name 2, column name 3 ... Column name n from table name

To alias a queried column:

Mode 1, original column name as ' Alias '

Mode 2, the original column name ' Alias '

Mode 3, alias = original column name

Get current system time:

Select Current system time =getdate ()

Calculation:

Select

======top data Query ======

Sort:order BY column name Desc (descending)/asc (ascending) default to Ascending

For the first few data, top is typically used with order by:

Select top value the data to be queried from table name order by column to sort Asc/desc

======distinct data Query ======

Data deduplication for the entire result set that has been queried:

SELECT DISTINCT * FROM table name

Chapter 3. Data retrieval (query)---Select, top, DISTINCT