Expression-Based GROUP BY

Function

This statement is used to group a table according to expressions.

Syntax

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SELECT attr_expr_list FROM table_reference
  GROUP BY groupby_expression [, groupby_expression, ...];

Keywords

The groupby_expression can contain a single field or multiple fields, and also can call aggregate functions or string functions.

Precautions

• The to-be-grouped table must exist. Otherwise, an error is reported.
• In the same single-column group, built-in functions and self-defined functions are supported in the expression in the GRUOP BY fields that must exit in attr_expr_list.

Example

To use the substr function to obtain the string from the name field, group the student table according to the obtained string, and return each sub string and the number of records, run the following statement:

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SELECT substr(name,6),count(name) FROM student
  GROUP BY substr(name,6);