Aggregate Functions

Updated on 2024-12-06 GMT+08:00

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**Table 1** Aggregate functions
No.	MySQL	GaussDB	Difference
1	GROUP_CONCAT()	Supported.	If the group_concat parameter contains both the DISTINCT and ORDER BY syntaxes, all expressions following ORDER BY must be in the DISTINCT expression. group_concat(... order by Number) does not indicate the sequence of the parameter. The number is only a constant expression, which is equivalent to no sorting. The data type of the return value of group_concat is always text regardless of the data type of the parameter. For MySQL, if group_concat contains binary parameters, the return value is binary. In other cases, the return value is a character string. If the return value length is greater than 512 bytes, the data type is a character large object or binary large object. The value of group_concat_max_len ranges from 0 to 1073741823. The maximum value is smaller than that of MySQL.
2	DEFAULT()	Supported.	The default value of a column is an array. GaussDB returns an array. MySQL does not support the array type. GaussDB columns are hidden columns (such as xmin and cmin). The default function returns a null value. GaussDB supports default values of partitioned tables, temporary tables, and multi-table join query. GaussDB supports the query of nodes whose column names contain character string values (indicating names) and A_Star nodes (indicating that asterisks [] appear), for example, default(tt.t4.id)* and *default(tt.t4.)**. For invalid query column names and A_Star nodes, the error information reported by GaussDB is different from that reported by MySQL. When the default value of a column is created in GaussDB, the range of the column type is not verified. As a result, an error may be reported when the default function is used. If the default value of a column is a function expression, the default function in GaussDB returns the calculated value of the default expression of the column during table creation. The default function in MySQL returns NULL.

Parent topic: System Functions

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