array_agg

Description

Aggregate the values including NULL in a column into an array. This way, you can turn values from a column to a row.

Syntax

ARRAY_AGG(col)

Parameters

col: the column whose values you want to aggregate. Supported data types are BOOLEAN, TINYINT, SMALLINT, INT, BIGINT, LARGEINT, FLOAT, DOUBLE, VARCHAR, CHAR, DATETIME, and DATE.

Return value

Returns a value of the ARRAY data type.

Usage notes

• The order of the elements in an array is random, which means it may be different from the order of the values in the column.
• The data type of the elements in the returned array is the same as the data type of the values in the column.

Examples

Take the following data table as an example:

mysql> select * from test;

+------+------+

| c1   | c2   |

+------+------+

|    1 | a    |

|    1 | b    |

|    2 | c    |

|    2 | NULL |

|    3 | NULL |

+------+------+

Example 1: Group the values in column c1 and aggregate the values in column c2 into an array based on the grouping of column c1.

mysql> select c1, array_agg(c2) from test group by c1;

+------+-----------------+

| c1   | array_agg(`c2`) |

+------+-----------------+

|    1 | ["a","b"]       |

|    2 | [null,"c"]      |

|    3 | [null]          |

+------+-----------------+

Example 2: Use the WHERE clause when the values in column c2 are aggregated into an array. If no data in column c2 meets the condition that is specified in the WHERE clause, a NULL value is returned.

mysql> select array_agg(c2) from test where c1>4;

+-----------------+

| array_agg(`c2`) |

+-----------------+

| NULL            |

+-----------------+

Keywords

ARRAY_AGG, ARRAY