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This article mainly introduces when to use table aliases in SQL query, the article is very detailed, has a certain reference value, interested friends must read it!

When do I need to use a table alias in a SQL query?

1. When the table name is very long

Select * from www_baidu_user where www_baidu_user.id = 1

And

Select * from www_baidu_user u where u.id = 1

The result of the query is the same, but the second one is more concise when using the table alias. Similarly, the same principle applies to aliases for fields.

2. When aliases must be used

As follows:

1)

Select * from (select * from table1) as T1

This is to query all the data directly from the subquery. You need to alias the table.

2)

Select b.name id,a.job,a.sex from An a left outer join B b on b.id = a.id

This is to query a column or columns of data, such as there is no name field in A table, the query must be accompanied by the table name or table alias, join queries are often used.

The above is all the contents of the article "when do you need to use a table alias in a SQL query?" Thank you for reading! Hope to share the content to help you, more related knowledge, welcome to follow the industry information channel!

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