The ROW data type was introduced in MariaDB 10.3.0.
 
Syntax
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ROW (  [{,  }... ])
 
Description
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ROW is a data type for stored procedure variables.
 
Features
 
ROW fields as normal variables
 
ROW fields (members) act as normal variables, and are able
to appear in all
query parts where a stored procedure variable is allowed:
Assignment is using the := operator and the SET command:
 
a.x:= 10;
 
a.x:= b.x;
 
SET a.x= 10, a.y=20, a.z= b.z;
 
Passing to functions and operators:
 
SELECT f1(rec.a), rec.a

URL: https://mariadb.com/kb/en/row/