stringagg

STRINGAGG is a string aggregation function for concatenating values from multiple rows into a single string with a chosen delimiter. It is widely used to produce comma-delimited lists of names, tags, or categories from a table.

The feature is implemented in several relational database systems under different names. In SQL Server, the function is STRING_AGG(expression, separator); in PostgreSQL it is string_agg(expression, delimiter). Other systems provide similar capabilities with LISTAGG (Oracle) or GROUP_CONCAT (MySQL). The exact syntax and optional ordering behavior vary by system.

Examples:

SQL Server: SELECT STRING_AGG(Name, ', ') AS AllNames FROM Employees;

PostgreSQL: SELECT string_agg(Name, ', ') AS AllNames FROM Employees;

To control order in PostgreSQL you typically wrap the table in a subquery with ORDER BY before applying the aggregate.

Oracle: LISTAGG(Name, ', ') WITHIN GROUP (ORDER BY Name) achieves the same result.

Notes:

NULL values are generally ignored by the aggregate. The function returns a string whose length is implementation-dependent and may be limited by the database’s maximum string length. For very large results, consider alternative approaches or ensure the result size fits the target system’s limits. STRINGAGG is commonly used for summarizing related rows, such as listing all tags for an item or all members of a group.