数据库查询语句 as union all

The "AS" keyword in database query language is used for aliasing. It allows you to rename a column or table with a new name. For example:

SELECT column_name AS new_name FROM table_name;

This query will select the column named "column_name" from the table "table_name" and rename it as "new_name".

The "UNION ALL" keyword is used to combine the results of two or more SELECT statements into a single result set. It returns all rows from each SELECT statement, including duplicate rows. For example:

SELECT column1 FROM table1
UNION ALL
SELECT column1 FROM table2;

This query will select the "column1" from "table1" and combine it with the "column1" from "table2" to create a single result set containing all rows from both tables.