Solution to Field Mismatch when Union all is used for query

A small problem may be solved by the definition limitation thinking in the book.

Definition:

The union or union all operator is used to merge the result sets of two or more select statements.

Note that the SELECT statement inside the Union must have the same number of columns. Columns must also have similar data types. In addition, the columns in each select statement must be in the same order.

Scenario:

When there are differences between individual fields in the two select result sets, union or union all is required.

Solution:

A small field in a result set can be replaced by a null value or a fixed value, and the alias is used to meet the consistent requirements of the column name.

To merge the result of student and teacher, the teacher wood has the name column.

Select name, age from studentunion allselect 'none' as name, age from teacher

Note:

There may be Type Mismatch. In this case, you only need to use cast () for type conversion.

Solution to Field Mismatch when Union all is used for query